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COFWRIGHT DEPOSnV 



THE 

MECHANICAL ENGINEERING 

OF 

STEAM POWER PLANTS 



BY 
FREDERIC REMSEN HUTTON, E.M., Sc.D. 

PROFESSOR EMERITUS OF MECHANICAL ENGINEERING IN COLUMBIA UNIVERSITY 

PAST PRESIDENT AND HONORARY SECRETARY OF THE 

AMERICAN SOCIETY OF MECHANICAL 

ENGINEERS 



THIBD EDITION REWRITTEN 

FIRST THOUSAND 



NEW YORK 

JOHN WILEY & SONS 

London : CHAPMAN" & HALL, Limited 

1908 



^^^4^ 



LIBRARY of CeNGRE6s) 
i wo Copies HectMvtfci 

SEP .24 )yob 

GLASS <X UC Nu 

COPY a. 



Copyright, 1897, 1906, 1908 

BY 

F. K. HUTTON 



Stanbopc iPress 

F. H. GILSON COMPANY 
BOSTON. USA. 



PREFACE 



The Power Plant lies at the basis of the comfort and the life of a 
modern community, and has an interest for nearly every one. There 
are, however, six groups whom it concerns specially. 

The first is the general public, who are supplied with light and power 
from it, for street transportation, in business and domestic economy, 
and in the railway, steamer, and motor vehicle; in the waterworks 
and the factory. To such, the one requisite is reliability; the stop- 
page or shutdown of the plant must not invade their comfort or con- 
venience in activities or pleasures, in their wage-earning or their safety. 

The second group is the business man of the investor or stock-hold- 
ing class, who has put capital into the power plant, or into the factory 
which rests upon it. His object is the sale of his product, either in 
the form of energy or horse power to users of power, or to the other 
departments of the works which it serves. He also is mainly concerned 
with the reliability of the plant, both because a stoppage means a loss 
of income directly, or a future loss in good- will ' towards his invest- 
ment; but in addition he must demand that the design and combina- 
tions in the plant are in accordance with advanced applications of 
science in order that efficiency and economy shall be attained, and these 
to the degree that he can still produce at a profit when the market price 
of his power commodity shall be low. He will not be a designer him- 
self, but will get his designing from others whom he pays. 

The third class will be the power-house operators, or engineers-in- 
charge. Their interests are the same as those of the investors as re- 
spects reliability and economy, with the added one of convenience, 
since these must stand by and maintain the efficiency of the plant as 
the object of their daily toil. They will not be designers or creators as 
a rule, but are often charged with the responsibility of critical selection 
from competing apparatus, and to do the duty of the consulting engi- 
neer for the second class. Of all the classes, these perhaps have the 
keenest personal interest and touch with the problem. 

The fourth class may be called the contractors. These are not' pri- 
marily users of the plant, but are business men who make a specialty 
of the design, erection, and sale of complete installations. They do not 



iv PREFACE 

usually create the details which they combine into a harmonious whole, 
although they may manufacture certain elements. They will have 
engineers of the highest grade working with and under them, as co- 
ordinators of design, and may be engineers themselves. In this class 
are district managers of large producing concerns, certain sales-man- 
agers and agents. Their interests are in reliability, economy, and 
acceptability as in the previous group, since the continuity of their busi- 
ness is involved in satisfying their customers and the consequent 
reputation. The consulting engineers in this fourth class will be 
representatives of the seller of the plant. 

In a fifth class will be the consulting engineers representing the 
buyers. These will rarely be creative designers of detail, but as 
office practitioners will write specifications and draw general plans, 
for the contractor class or productive manufacturers to meet. Their 
interests and requirements are the same as with the contractors, 
and for the same reasons. 

Finally, in the sixth class are the creative designers of the details 
in the plant, who are usually also producers or manufacturers, or who 
are employed by such as engineers or draftsmen. They are required 
to meet all the foregoing demands, and in addition to be consulting 
experts scientifically and professionally, and both as scientific men 
and shop executives. The demand for such men is continually nar- 
rowing the scope of the fifth group; and the commercial effectiveness 
of business done by the fourth group is as steadily broadening their 
field, and bringing the producer, who is also the creator through the 
engineers in his employ, into the first rank and securing increasing 
consideration for him. 

The student of engineering may become a member of any group 
of the foregoing. The broadest field for him on graduation and where 
he is best paid is in the growing fourth group. His study of the power 
plant may therefore wisely be directed to fit him for usefulness in that 
class, leaving his later specialization in design or creation to be the 
result of circumstances in his life. 



The view-points for power-house problems are two. The one is the 
functional requirement : what is to be accomplished, and what apparatus 
is needed to do this work. The other is quantitative : how large must 
the apparatus be to do a certain quantity of such required work. Plainly 
the first three groups are concerned only with the first; and only the 
engineers of the fourth group with the second. The engineers and 
designers of the sixth class are mainly concerned with proportions or 



PREFACE V 

quantities; but they also must begin the study of their specialty at 
the functional end, which will be the basis for quantitative design in 
any case. Hence the object of this book is largely the study of func- 
tion and purpose of power-plant apparatus. It is not to be regarded 
as a- treatment of design of the elements of the power plant, but only 
of the power plant as an aggregate of elements. To have included 
machine design would have rendered its real contents hard to get at 
in the multiplicity of topics, and would have made the conditions 
prohibitory as respects size and price. Furthermore, power-plant 
design should be taken up with a more mature knowledge than is sup- 
posed to belong to the beginner, and should cover many matters dif- 
ficult to treat fairly in a text-book. The last chapter is intended 
as an open door to some of these questions, and for more advanced 
students. 

The basis of theoretical mechanics under some elements of power- 
plant practice has been given in smaller type than the main trend, so 
that those to whom it is of secondary interest may skip it without 
sacrifice of continuity. 



A former edition of this book, issued in 1897, embodied the study and 
experience of the author gathered during the previous twenty years and 
brought together for teaching purposes. The years since then have 
been a period of great and rapid progress in the power plant and in 
all engineering departments contributory thereto; and while the old 
edition was modernized here and there and year by year, the time had 
come with the opening decade of the twentieth century that it be re- 
written entirely. The present edition is the result of such rewriting. 

It is a new book so much enlarged that the old plates could not be 
used, but the size of page has been increased, new illustrations chosen, 
and many new topics and treatments have been introduced. While 
the former approved analytical view-point is retained and amplified, 
there has also been introduced a discussion in many chapters of the 
principles and data of applied mechanics attaching to the subject in 
hand. This has been done to enable teachers who desire to enliven 
the drill in the mathematical classes to find practical problems and 
applications of interest and future meaning, and to encourage teachers 
of the applications of theory to find easily the links and bases for such 
sound applications. The distinction between the applied thermal prin- 
ciples and those derivable from other departments of theory should 
tend also to clearness and benefit. 

The new treatments which are specially noteworthy are those of 



Vi PREFACE 

the analysis of the power plant and its diagram, and the separation 
between the simple and the complex phases of this problem; the 
treatment of the steam pipe as an element of co-ordinate importance 
in the plant with the boiler and the engine; the chapters on the aux- 
iliaries as distinguished from the essentials; the steam turbine chap- 
ter, the engine mechanism chapter, and the establishment of the phil- 
osophy of the expansion of the elastic medium as the basis for the 
valve gear, the governor, the condensing and the compound engine. 
This is new, and it is believed that it will be helpful and illuminating. 
Some data and tables have been introduced, but only sparingly. The 
author prefers that students should acquire the habit of going to the 
^'Engineers' Pocket Books" for statistical or quantitative information, 
using this book to give a perspective or setting to make clear the 
meaning and interpretation of such data and constants as these 
excellent books are prepared to furnish. 



The book has been written with other objects as well as for its use 
as a text-book in schools of engineering. But the recognition of the 
basal and fundamental importance of the power plant in all kinds 
of engineering enterprises has necessarily given this possible use a 
great share of consideration. It may not be amiss therefore to sug- 
gest some methods for such use which have been tried out in the 
author's experience, and have been before his mind in preparing the 
text. 

1. The primary purpose of the educational process should be to 
make the learner think. While it is true that knowledge is power, 
such knowledge and power are only really possessed for any time by 
him whose faculties have exercised themselves in the process of de- 
ducing principle from fact. Hence the recitation process is far to be 
preferred to the lecture method of instruction in such a subject as 
this. 

2. The recitation method at the blackboard by sketch or upon 
the drawing-pad is far the best. The sketch cannot be vague or in- 
definite, and hence the knowledge which it reveals must be equally 
precise and definite. This in itself has an educational value. 

3. The reproduction of the illustration in outline should be so done 
that the principle is laid bare, and the accidental or accessory detail 
is relegated to second place or omitted. The illustrations have been 
chosen to favor this procedure; and old cuts have been retained even 
when newer practice differs from the old, where the principle was 
clearer in the old than it would have been in the new. This explains 



PREFACE Vii 

further the copiousness of illustration; it justifies the use of figures 
from commercial sources as giving living and present interest to what 
might else be dry and unattractive. 

4. The instructor should reaUze that in any class the number is 
small who will be called on to design and construct any detail of the 
power plant; but that all are sure to be called on to buy some or all 
of these elements, or to design power plants as a whole, in which such 
elements are to function. Hence the training in the process of selec- 
tion, of critically weighing arguments for and against an apparatus, 
and evaluating advantages and disadvantages, becomes a most valuable 
discipline. The treatments designed to this end should be diligently 
so used. 

5. It would be impossible to make the treatment and particularly 
the illustrations cover every embodiment of principle which is now 
in use. The book would exceed the intelligent limits of size and price 
with even current practice; and the progress of science, invention, and 
design is continually bringing new material. The instructor is urged 
to bring such new illustrations into class in the form of photographs, 
lantern-slides, trade-catalog literature, and the articles from the 
technical press and society proceedings; and to use them in the same 
way as in Nos. 2, 3, and 4 above in supplement to what the text covers. 
The country is so large that standard practice in one section may not 
be well known in another, but a broad view requires consideration of 
all practical solutions. 

6. For the more advanced student whose instruction should be more 
personal, and in seminars or conferences, there are no better text- 
books to suggest topics for discussion than the technical newspapers 
and magazines. These offer up-to-date and live issues, new prob- 
lems and their solutions, accidents and failures, queries and opinion. 
But to utilize such material by partly trained students or those hav- 
ing limited experience only, recourse should be had to fundamental 
principles, accepted standards, and the teachings of the past and of 
experience. For such elements the treatments of this book may be 
conveniently used, and such advanced students will find more material 
upon a re-study than they found in the first contact with the text. 

7. It is an admirable drill in the thought-compelling process and 
for its impress on the student, to compel him to formulate the ques- 
tions upon the sketch or illustration. This can be done most effect- 
ively by the lantern-slide, exhibited by an electric projection lantern to 
a whole class in a room not wholly darkened. If one student- can 
ask the questions for another to answer, not only is the answerer forced 
to think, but the questioner even more. The instructor can reach the 



VIU PREFACE 

perspective and view-point of the class for a guiding and stimulation 
of the discussion and for an effective summing up. 

8. Finally, there is no engineering literature of greater teaching 
value than the specifications which have been used in successful prac- 
tice. To use and digest these, however, a certain previous knowledge 
is requisite. If the student can have these specifications given to him, 
and be compelled to defend the requirements therein set forth on the 
basis of discussions in such a text-book as this, he receives an un- 
equaled training for his future work. Advanced students can be 
drilled with specifications in evaluating alternate requirements, on the 
basis of what they can find in the fundamental treatments in the text. 



The critical student of power-house problems may propound two 
questions: Is not the development of the steam turbine to render 
valueless a treatise of this sort in a year or two, in so far as it relates 
to the reciprocating engine? and will not the spread and development 
of the internal combustion motor or gas engine render valueless the 
space devoted to both boiler and steam engine? 

There are several categories to the answer to the first question: 

1. The turbine will not displace the reciprocating engine in cases 
where the starting resistance is high at necessarily low speed* of turning. 

2. The turbine is not so much better in economy or convenience than 
a good economical reciprocating engine that owners and users are 
going to displace the latter. The turbine may be installed for new 
developments, but the reciprocating engines will run for years yet. 

3. The turbine is at its best for electrical transmission of the power: 
where some other medium is better the reciprocating engine will remain. 

4. The turbine is at its best for large units; for small and medium 
conditions the reciprocating engine still has a field of its own. 

5. Everything in this treatise concerning the boiler, the piping, and 
the auxiliaries remains untouched by such a change if it occurs. Per- 
haps the auxiliaries receive enhanced importance in a turbine plant, 
and what attaches to the details of the main motor herein will be 
equally true for the greater part of the enlarged auxiliaries. 

6. The turbine will not displace the reciprocating engine where the 
resistance must be slow-moving, calling for a gearing down of the 
speed of the motor element. 

7. The most complete disappearance of the reciprocating steam 
engine will occur, if at all, when all industry is carried on by transmit- 
ting electrical energy distributed from central generating stations. The 
driving engines in these central stations will be turbines or gas engines, 



PREFACE ix 

and there will be no isolated or independent steam engines at all, in 
the plants of individual parties. 

The second question, concerning the vogue of the gas engine, is also 
one which' is not to be answered by a single sentence. 

1. . There is no doubt that enormous increase is to be foreseen in the 
use of the small internal combustion engine using carbureted air from 
liquid fuel. This will be in motor boats, in motor vehicles, in railway 
branch service, and in stationary practice, and it will displace the small 
steam engine and be used in places where the reciprocating engine will 
not go. 

2. But for large installations, the cost of liquid fuel compared with 
coal becomes prohibitory under economic conditions, and the gas pro- 
ducer must be provided. As soon as this happens, many advantages 
of the gas engine begin to balance up with those of the steam plant, 
although the avoidance of the auxiliaries of the steam plant leaves a 
heavy balance in favor of the other system. 

3. But when the largest size of generating unit is called for, the big 
gas engine meets its limiting condition, just when the steam engine is 
reaching its best. The problem of cooling the big engine with a large 
diameter cylinder, and disposing of the great quantity of heat released 
in the combustion of masses of gas, introduces difficulties with the gas 
engine which are not yet solved, and perhaps are not going to be. The 
big gas engine becomes costly, bulky, and occupies great space. Repairs 
and maintenance mount up; auxiliaries for starting appear, and the 
advantages of the big steam plant begin to emerge anew. 

4. Finally, in any industry where the exhaust from the steam engine 
is required in the industrial process for heating solutions, or for drying 
as in the paper and textile industries, or for the heating of buildings 
in winter as in the office-buildings of the congested cities, the steam 
engine as source of needed power will have the balance in its favor. 

The gas turbine, if it becomes reahzable by discovery of new laws or 
methods to avoid the prohibitive action of known old ones, will of 
course revolutionize many departments. But until these steps are taken 
there will be some time during which the steam engine will justify the 
study this book encourages and provides for. 



The writer of to-day is under profound obligations to those who have 
preceded him, and this edition in particular owes much to writers whose 
work has appeared since the earlier publication was made. Besides 
repeating the acknowledgments of the earlier edition, special recognition 
should be made for valuable co-operation from Mr. Charles L. Hubbard, 



X PREFACE 

author of " Power Heating and Ventilation;" from Mr. Lester G. French 
and Prof. C. C. Thomas in the discussion of the steam turbine; from Mr. 
Henry C. Meyer, author of '' Power Plants," and to their publishers 
for permission to make use of cuts in convenient form. The help of 
manufacturers and designers is also gratefully acknowledged in the 
matter of illustrations and special designs of such producers. Prof. 
John Goodman of Leeds, and Prof. John Perry of London, England, 
have been strong influences upon the author in his more mathematical 
discussions of topics, and he is glad to recognize these obhgations. He 
would heartily thank those instructors and other users of the text-book 
for their appreciative comment and helpful criticism. 

Attention should finally be called to the re-arrangement of topics, 
whereby the boiler and its accessories has been made to precede the 
engine and its problems. This will be found to offer a teaching advan- 
tage in that the phenomena of the boiler and combustion belong to the 
simpler problems of chemistry, physics, and mechanics, and their study 
can begin early in a progressive course. The moving engine using 
transformed heat in the form of pressure and changing pressure into 
work compels an outlook upon the principles and data of thermo- 
dynamics, and is conveniently placed later where greater maturity and 
a wider range of study will permit the theory and the practice to be 
more effectively co-ordinated than with the older arrangement upon 
a different logical basis. Hence also much of the book can be made to 
precede the study and practice of the practical or experimental engineer- 
ing laboratories of the schools, as well as courses in engineering design 
on the drawing board; and with manifest advantage. 

It is the wish and hope of the author that the material here brought 
together and the methods of treatment may be found serviceable in 
the work of engineering education to which he has given so many happy 
years. 

F. R. HUTTON. 

New York City, 

September, 1908. 



TABLE OF CONTENTS. 



PART I. 

Introductory. 

PAGE 

1. The Function of the Power Plant. , , 1 

2. Sources of Motor Energy for the Power Plant. Internal and 

External CombustioiT 2 

3. Measurements of the Work Unit of Output. Indicated Horsepower, 

Brake Horsepower 3 

4. Elements and Analysis of the Steam Power Plant 4 



CHAPTER I. 

The Quantitative Basis of the Steam Power Plant. 

5. Introductory . 10 

6. The Horsepower of a Piston Motor. The Cylinder Volume 10 

7. The Work Unit and Heat Unit are Convertible. The Volume of 

Steam per Horsepower 12 

8. The Water Rate of Steam Engine 13 

9. The Heating Surface of a Steam Boiler. Transfer of Heat 14 

10. The Horsepower of a Boiler. A.S.M.E. Standard. 15 

11. The Pounds of Coal to Evaporate a Weight of Water 16 

12. Grate Surface to Burn a Weight of Fuel in a Given Time. Rate of 

Combustion 16 

13. The Cost of a Horsepower 18 

14. Summary and Conclusions 18 



PART II. 

CHAPTER II. 

The Boiler. Forms, Material and Manufacture. 

20. Introductory . 19 

21. The Function of the Boiler or Steam Generator ...._. , , . 19 

22. The Storage of Energy in a Steam Boiler 20 

23. The Problems of Physics respecting Transfer of Heat . 23 

xi 



xii TABLE OF CONTENTS 

PAGE 

24. Combustion 26 

25. The Problems of Mechanics respecting Form and Internal Stress. 26 

26. Values of the Stresses in Boiler Shells. Thickness of Boiler Plate ... 28 

27. Materials for the Boiler Shell. Specifications and Tests 30 

28. Shaping the Shell Elements. Curving Plates 32 

29. Arrangement of Rings of Plate in Shells 34 

30. Shaping the Shell Elements. Flanging Heads . 35 

31. Joints in Boiler Shells. Welding 37 

32. Riveted Joints for Boiler Shells 39 

33. Construction of a Riveted Joint. Punching and Drilling 40 

34. Punching and Drilling Compared 41 

35. Hand and Machine Riveting ? . 43 

36. Mechanics of the Stress in a Thin Cylinder 47 

37. Copper, Cast Malleable and Wrought Iron for toiler Shells 47 



CHAPTER III. 
Boiler Riveting, Staying, and Structural Details. 

40. Mechanics of the Riveted Joint. Efficiency 49 

41. Arrangement of Rivets in a Joint. Special Joints 51 

42. Failure of the Riveted Joint 56 

43. The Drift Pin '. 56 

44. Stays and Staying , .... 57 

45. Manholes . 66 

46. Handholes 70 

47. Edge-Planing and Calking 70 

48. Disengagement-Area, Water Space and Steam Space 72 

49. Domes and Steam Drums 73 

50. Mud-drums 79 

51. Concluding Comment. Classification of Types 80 

CHAPTER IV. 
Fire-Tube Boilers Externally Fired. 

55. Types of Boiler in the Fire-tube Class 84 

56. The Tubular or Multitubular Type 84 

57. The Tubes for Fire-tubular Boilers 87 

58. Ribbed Tubes. Retarders 90 

59. Arrangement of Fire-tubes 90 

60. The Fhie Boiler 92 

61. Reinforced Flues for Long Boilers 95 

62. Conditions Suggesting Choice of Tubular or Flue Types . , 96 

63. U. S. Formulae for Flues 97 



TABLE OF CONTENTS xiii 

CHAPTER V. 
Fire-Tube Boilers. Internally Fired. 

PAGE 

65. Definition of Internal Firing. Advantages and Disadvantages of the 

. Principle 100 

66. The Cornish and Lancashire Boiler 102 

67. The Galloway Tube in Lancashire Boiler 103 

68. The Scotch or Cylindrical Marine Boiler 103 

69. The Rectangular Marine Boiler 107 

70. The Locomotive Boiler 109 

71. The Locomotive Boiler with Corrugated Furnace 116 

72. Derivatives of the Locomotive Boiler , : 119 

73. The Upright Boiler 120 

74. Modifications of the Upright Boiler 126 

75. The Fire-engine Boiler 127 

76. Combinations of Type 129 

CHAPTER VL 

Water Tube Boilers. 

80. Introductory. , 130 

81. The Plain Cylinder Boiler 132 

82. The Elephant Union and French Boiler 132 

83. The Sectional Principle 134 

84. Advantages of the Sectional Principle 134 

85. Disadvantages of the Sectional Principle . 135 

86. Classes of Sectional Boiler 137 

87. Spheroidal Unit Type 138 

88. Vertical Straight Open Tube Type 140 

89. Horizontal Straight Open Tube Type 141 

90. Vertical Curved Open Tube Type 149 

91. Horizontal Curved Open Tube Type 152 

92. Closed Straight Vertical Tube Types. Field Tubes 152 

93. Closed Straight Horizontal Tube Types 154 

94. Bent or Curved-Tube Types 154 

CHAPTER VII. 
Coil and Pipe Boilers. Flash and Semi-Flash Boilers. 

95. Introductory 155 

96. Tube -and -Fittings Boiler 155 

97. The Coil Boiler 156 

98. Sundry Types. Conclusions 157 

99. Spray Boilers 160 

100. Flash and Semi-Flash Boilers 160 



XIV TABLE OF CONTENTS 

CHAPTER VIII. 

Boiler Furnaces, Chimneys and Setting. 



PAGE 



105. The Fire as the Source of Energy 165 

106. Principles Underlying the Boiler Grate 167 

107. Principles Underlying the Chimney 167 

108. Discussion of Peclet's Theory of Chimney Draft 170 

109. Some Accepted Chimney Formulae and Data 171 

110. Dilution of the Products of Combustion 174 

111. The Grate Bars. Stationary Grates 174 

112. Shaking and Dumping Grate Bars 176 

113. Step Grates : 179 

114. Mechanical or Traveling Grates. 179 

115. Mechanical Stokers 181 

116. Inclined and Horizontal Grates 181 

117. The Firing on the Grates 184 

118. The Dead-plate and Furnace Mouth-piece 184 

119. The Ash-pit 186 

120. The Bridge-wall 187 

121. The Combustion Chamber 190 

122. The Back Connection 194 

123. The Front Connection 195 

124. The Flue to the Chimney-stack 195 

125. The Damper and Damper Regulator '. . . . 196 

126. The Chimney 198 

127. Artificial or Mechanical or Forced Draft 202 

128. Advantages of Artificial Draft 205 

129. Disadvantages of Artificial Draft 206 

130. Smoke prevention 208 

131. Boiler Setting. Side walls 215 

132. Buck Stays and Tie-Rods 217 

133. Hanging of Boilers 218 

134. Boiler Fronts 220 

135. Concluding Comment. Gallows Frame Supports 225 



CHAPTER IX. 

Firing Boilers with Gas or Liquid Hydrocarbon or with Pulverized 

Fuel. 

136. Introductory 227 

137. Gas Firing of Boilers 227 

138. Liquid Fuel Burners 228 

139. Liquid Fuel Furnaces 230 

140. Precautions in Oil Firing 231 



TABLE OF CONTENTS XV 

PAGE 

141. Advantages of Oil Fuel , 232 

142. Disadvantages of Oil Fuel 233 

143. Pulverized Fuel Systems 234 

144. Sundry Special Fuels 234 

145. Conclusion. Heat Balance , 236 



CHAPTER X. 
Boiler Accessory Apparatus. 

146. Introductory 240 

147. The Feed-Pump , 240 

148. The Attached Pump or the Independent Feed-Pump 241-3 

149. -The Fly-Wheel Pump 244 

150. Direct Acting Pump 245 

151. The Feed Pipe and its Valves 249 

152. Introduction of the Feed Water 250 

153. Blow-off Pipe 252 

154. Loss in Blowing-ofi 253 

155. The Injector 253 

156. Mechanical Principles underlying the Injector. Induced Current 

Principle o 255 

157. Heat Transfer; Work and Efficiency in the Injector 256 

158. Mechanical Principles of Impact in the Injector 257 

159. Double Tube Injector. The Inspirator 258 

160. Re-starting or Automatic Injectors 259 

161. Exhaust Steam Injectors 260 

162. Advantages of the Injector , 260 

163. Disadvantages of the Injector 260 

164. Water Gages 260 

165. The Glass Water Gage and Water Column .' . . 261 

166. The Gage-Cocks 266 

167. Float Water Gages .' 266 

168. Low Water Alarms 268 

169. Fusible or Safety Plugs 268 

170. Automatic Feeding Apparatus 269 

171. The Steam Gage 271 

172. Standardizing or Calibration of Steam Gages 274 

173. Recording Gages 274 

174. The Relief or Safety Valve , . 275 

175. Forms of Safety Valve 275 

176. Safety Valve Formulae , 277 

177. Computations for the Lever Safety Valve 278 

178. Concluding Comment 278 



XVI TABLE OF CONTENTS 

CHAPTER XL 
Care and Management of Boilers. 



PAGE 



180. The Firing 279 

18L Cleaning Fires 279 

182. Banking Fires 280 

183. Regulation of the Fire and Pressure of Steam , 280 

184. Cleaning the Heating Surface Outside 281 

185. Boiler Scale or Incrustation 282 

186. Inconveniences Due to Boiler Scale 285 

187. Removal of Boiler Scale 286 

188. Prevention of Scale Formation , 287 

189. Previous Purification of Feed Water • • 290 

190. Filtration of Feed Water 291 

191. Determination or Wear and Tear of Boilers 292 

192. Overheating of Boilers 292 

193. Unequal Expansion and Contraction of Boilers 292 

194. Corrosion External 293 

195. Corrosion Internal 294 

196. Pitting, Wasting and Grooving 295 

197. Repairs General. 296 

198. Patches 297 



CHAPTER XII. 
Boiler Inspection and Testing. Boiler Explosions. 

200. Boiler Inspection. 298 

201. The Steam Pressure Test 298 

202. The Hot Water Pressure Test 299 

203. The Cold Water or Hydrostatic Test , . 299 

204. The Hammer Test ' 299 

205. Boiler Explosions. General 300 

206. Boiler Ruptures because too Weak 300 

207. Boiler Ruptures from Excess of Pressure 301 

208. Theory of Boiler Explosions 302 

209. Energy Resident in Hot Water under Pressure 302 

210. Reaction in Boiler Explosions 303 

211. Procedure when a Boiler is in Danger of Rupture 303 

212. Heating Effect of Steel Plate and Cooling Effect of Water 304 

213. Time Required by Boiler to absorb Heat and Pressure Energy 304 

214. Steam Boilers as Magazines of Explosive Energy 305 



TABLE OF CONTENTS xvii 

PART III. 

CHAPTER XIII. 
Boiler Plant Auxiliaries. 

PAGE 

220. Introductory 306 

221. Coal Handling Machinery 307 

222. Ash Handling Machinery 308 

223. Mechanical Stokers 309 

224. The Forced or Induced Draft by Fan and Motor or Engine 315 

225. Preheating of Feed Water 315 

226. Flue Heaters or Economizers 316 

227. . Exhaust-steam Feed Water Heaters 317 

228. Superheating of Steam 321 

229. Methods of Superheating 325 

230. Advantages of Superheating 327 

231. Disadvantages of Superheating 329 

232. Combustion Indicators 330 

233. Water Meters 332 

234. Concluding Comment 334 



PART IV. 

CHAPTER XIV. 
The Piping of Pressure to the Engine and its Accessories. 

235. General. 335 

236. The Stresses in a Steam Pipe and its Requirements 336 

237. The Material for a Steam Pipe 339 

238. Steam Pipe Joints and Fittings 340 

239. Expansion of the Steam Pipe by Heat 345 

240. Hangers and Carriers for Steam Pipe 347 

241. Valves for Steam Pipe 348 

242. Grading of Steam Pipe 354 

243. Drainage of Steam Pipe. Separators 354 

244. Non-conducting Coverings for Steam Pipe 360 

245. Exhaust Pipe 362 

246. Oil Separators 363 

247. Exhaust Heads 366 

248. Back-pressure valves 367 

249. Reducing valves 368 

250. Drip-Connections 369 

251. Concluding Comment 369 



xviii TABLE OF CONTENTS 

PART V. 

CHAPTER XV. 
The Engine. 

PAGE 

254. Introductory _ . 371 

255. The Ordinary Steam Engine 372 

256. The Kinematics of the Crank-connecting-rod Mechanlsmo Some 

Engine Mechanisms 376 

257. Deductions from the Kinematic Chain of the Steam Engine 385 

258. Effectiveness of the Crank-connecting-rod Mechanism 387 

259. Dynamic Stresses in the Mechanism of the Typical Steam Engine 390 

260. Inertia and Acceleration of the Reciprocating Parts of a Steam 

Engine 393 

261. Net Impelling Effort upon the Crank-Pin 395 

262. Relief of Crank-Pin Stress by Cushioning by Compression of Exhaust 

or Live Steam , 396 

263. The Turning Leverage or Torque of the Crank 398 

264. The Flinging or Slinging Stress in the Connecting-Rod 400 

265. The Accelerating Effort with Short Connecting-Rods 402 

266. Concluding Comment = . . . . . . . 404 



CHAPTER XVI. 
The Engine Continued. 

270. Introductory 405 

271. The Horizontal Engine 405 

272. The Vertical Engine ; 406 

273. Direct and Inverted Vertical Engines 408 

274. Inclined Engines 409 

275. The Horizontal-Vertical Engine 414 

276. Direct- Acting Engine 416 

277. Beam-Engines 416 

278. Structure of Beam Engines 417 

279. Objections to the Beam Engine, Side-lever Type 423 

280. The High Speed and the Low Speed Engine 426 

281. The Low Speed Engine 427 

282. Piston Speed Values in Feet per Minute 428 

283. Double and Single Acting Engines 429 

284. The Cornish Engine 429 

285. Operation of the Cornish Engine Cyhnder. 430 

286. Cataract of the Cornish Pumping Engine 431 

287. Advantages and Disadvantages of the Cornish Engine 432 



TABLE OF CONTENTS xix 



PAGE 



288. Single-£icting Rotative Engines 433 

289. Right-hand and Left-hand Engines 436 

290. Center and Side Crank Engines 438 

291. Sundry Mechanisms and Arrangements. 439 

292. Concluding Comment 441 

CHAPTER XVII. 
Expansive Working of Steam. 

295. Introductory. The Indicator „ . . . . 442 

296. Non-Expansive Working of Steam in the Cyhnder 444 

297. Efficiency in a Heat Engine 445 

298. Expansive Working of Steam in the Cyhnder 446 

299. Advantages of Expansive Working of the Steam . 447 

300. Disadvantages of Expansive Working of the Steam 448 

301. Numerical Values for Pressures and Work of Expanding Steam. . . . 450 

302. Weight of Steam Entering the Cylinder at Different Initial Pressures. 

Steam per Horsepower per Hour 452 

303. Cut-off and Ratio of Expansion. Most Economical Point of Cut-off 453 

304. Governing in Non-expansive Engines or with Fixed Cut-off. 

Throttling Governing 455 

305. Governing in Expansive Working of Steam. Automatic Cut-off 

Engines 457 

306. The Condensing Engine, with Lowered Back-pressure 460 

307. Disadvantages of the Condensing Engine 463 

308. The Compound Engine 465 

309. The Computation of the Mean Pressure in Expanding , . . 465 

CHAPTER XVIII. 
The Compound and Multiple Expansion Engine. 

315. Compound Engine Defined . 467 

316. Thermal Advantages of the Compound Engine 470 

317. Mechanical and Practical Advantages of the Compound Engine. ... 471 

318. Disadvantages of the Compound Engine ; 473 

319. Mechanisms of the Compound Engine 475 

320. The Tandem Engine. The Steeple Engine. Beam Compounds. . . . 478 

321. The Fore-and-Aft, or Side-by-Side Compounds 483 

322. The Cross-Compound Engine, Receiver Engine 484 

323. The Triple Expansion and Quadruple Expansion Engine. ......... 485 

324. The Compound Locomotive 485 

325. Compounding above the Atmosphere 490 

326. The Receiver and the Reheater . 490 

327. The Work and Indicator Diagram of a Compound Engine , . 492 

328. Concluding Comment 496 



XX TABLE OF CONTENTS 

CHAPTER XIX. 

The Rotary Steam Engine. 

PAGE 

330. Rotary Steam Engine Defined 497 

331. Types of Rotary Engine Mechanism 498 

332. Advantages of the Rotary Engine 502 

333. Disadvantages of the Rotary Engine 503 

CHAPTER XX. 

The Steam Turbine. 

335. Introductory. Historical 505 

336. The Mechanics of the Steam Turbine 506 

337. Impulse Energy against a Turbine Blade 506 

338. Reaction in a Jet and Bucket 508 

339. Relation of Jet Velocity to Pressure 508 

340. Blade Velocity under the Jets 509 

341. Thermodynamic Principles underlying the Steam Turbine 509 

345. Single Stage Expansion Nozzle Turbine 511 

346. Single Stage Impulse and Reaction Turbine without Expansion Noz- 

zle. Riedler-Stumpf Early Types 513 

347. The Pure Reaction Turbine without Impulse 514 

348. Compound Turbines. Multicellular Type 514 

349. Reaction in Steam Flow from a Stationary Guide Ring. Stator 

Rings 517 

350. The Westinghouse Compound Turbine 519 

351. Governing and Overload Capacity in the Westinghouse Turbine. . . . 519 

352. The AUis-Chalmers Compound Turbine 524 

353. The Curtis Nozzle Compound Turbine 525 

354. Governing and Overload in the Curtis Turbine 529 

355. Low Pressure or Exhaust Steam Turbines 529 

356. The Steam Turbine for Marine Use ' 530 

357. Advantages of the Steam Turbine 534 

358. Disadvantages of the Steam Turbine 537 

359. Costs of the Steam Turbine. 538 

360. Performance of the Steam Turbine 541 

361. Concluding Comment 542 

CHAPTER XXI. 

Engine Foundation and Bed-Plate. 

365. Introductory 544 

366. Mechanics of the Engine Foundation. Shaking Forces 545 

367. Construction of Engine Foundations 550 

368. Footings to Prevent Vibration 552 



TABLE OF CONTENTS XXI 

PAGE 

369. Foundation Bolts = 554 

370. Alinement of Foundation Template 555 

371. Locating the Bed-plate on the Foundation 556 

372. Alinement of Outer- Pillow Block or Shaft-bearing 558 

373. Forms of Engine Bed-plate, Horizontal Types 560 

374. The Bed or Frame of a Vertical Engine 568 

CHAPTER XXII. 
Engine Cylinder, Piston and Piston-Rod. 

375. The Cylinder Casting . 569 

376. The Counter-bore 574 

377. CyHnder-cocks and Relief or Snifting Valves 574 

378. The Cylinder Jacket or Lagging 575 

379. The Structure of the Piston 576 

380. The Piston Packing 578 

381. Piston Rings 581 

382. The Piston Rod 584 

383. The Stuffing Box 586 

384. Air Valves. , 591 

CHAPTER XXIII. 

Cross-Head, Guides, and Connecting-Rod. 

385. The Guides and Slides 592 

386. The Cross-head 595 

387. The Cross-head Pin or Wrist-pin 598 

388. Parallel Motions 595 

389. The Connecting-Rod. 599 

390. The Stub-end 600 

391. Forked-end Connecting-Rod. Double Rods 605 

CHAPTER XXIV. 

Crank-Shaft, Eccentric, Fly-wheel. 

395. The Crank-shaft . 607 

396. The Crank-pin . 608 

397. The Crank 608 

398. The Locomotive Crank and Shaft 609 

399. The Marine Crank-shaft 611 

400. The Main or Crank-Bearing 612 

401. The Eccentric 614 

402. The Eccentric-rod and Valve-stem 615 

403. The Fly-wheef 617 



XXll TABLE OF CONTENTS 



PAGE 



404. The Mechanics of the Fly-wheel 619 

405. The Stresses in Fly-wheels 622 

406. Solid and Segmental Fly-wheels 623 

407. Fly Band-wheels 626 

408. Steel Fly-wheels 626 

409. Composite Band Wheels 626 

410. Conclusion and General 627 

CHAPTER XXV. 

Valves and Valve Gearing. 

415. The Valve Gear and the Governor 628 

416. Engine Valves. General. Lifting or Poppet Valves 628 

417. Engine V-alves. Sliding, Rocking or Revolving Valves 630 

418. The Timing of the Valve. One, Two, Three and Four-Valve 

Systems 633 

419. Plain Slide Valve, Taking Steam Full Stroke 635 

420. The Eccentric is a Crank ; 637 

421. Setting of a Plain Slide-valve, working Non-expansively 638 

422. The B Valve 640 

423. Engine to use its Steam Expansively, at Constant Cut-off. Lap in 

the Slide- Valve 640 

424. Effects of the Lap : 641 

425. Inside Lap 642 

426. Effect of Inside Lap 642 

427. Exhaust Clearance, or Negative Exhaust Lap 643 

428. Lead in the Slide Valve 644 

429. Effects of Lead 644 

430. Setting of Slide Valve without Access to Valve-chest. Setting by 

Sound 645 

CHAPTER XXVI. 
Valve Gearing Design. Special Forms. 

435. The Zeuner Polar Diagram for Slide Valve Design 647 

436. Graphical Solution by the Zeuner Polar Diagram 649 

437. Use of the Zeuner Polar Diagram 651 

438. Valve Gear Problems and Design 652 

439. Limitations of the Single Slide Valve 653 

440. Valve-gear for High Degrees of Expansion. Two- valve systems 654 

441. Three and Four-valve Gears 657 

442. Shortening Steam Passages 657 

443. Shortening the Throw of the Valve. Allen Valve 658 

444. Gridiron Slide Valve 659 



TABLE OF CONTENTS Xxiii 

CHAPTER XXVIL 

Valve Gearing. Balanced Valves. Cam and Trip Valve-Gear. 

PAGE 

445. Balancing Slide Valves 662 

446. Piston Valves 663 

447.' Pressure Plate Systems 665 

448. Valves taking Steam Internally 669 

449. Valves with Counter-pressure 669 

450. Poppet Valves 670 

451. Cam Valve-gears 670 

452. Trip or Releasing Valve-gears 675 

453. Corliss Valve-gears 676 

454. Advantages of Trip Valve-gear 680 

455. Disadvantages of Trip Valve-gear 681 

456. Sundry Valve-gear , 681 



CHAPTER XXVIII. 
Reversing Valve Gears. Link Motions. 

460. Reversing Gears with One Eccentric 682 

461. Reversing Gears with Two Eccentrics. Gab-hooks 683 

462. Link-motion of Stephenson or Howe 685 

463. Features of the Stephenson Link-motion 686 

464. Gooch's Link-motion 688 

465. Allan's Link-motion 688 

466. Radial Valve-gear, Joy's Valve Gear 688 

467. Walschaert Valve-gear , 691 

468. Allen Link Motion. 691 

469. Link-motion for Riding Cut-off Valves 691 

470. Power Reversing Gears 693 



CHAPTER XXIX. 
Valve Gears for Variable Cut-off. 

471. Variable Cut-off and Throttling Control. 695 

472. Cut-off Varies by Varying Throw of the Valve 695 

473. Cut-off Varies by Varying Lap of Valve. „ 696 

474. Cut-off Varies by Varying Angular Advance of Eccentric 697 

475. Cut-off Varies by Varying Point of Release or Trip 698 



XXIV TABLE OF CONTENTS 

CHAPTER XXX. 

Governing and Governors for Steam Engines. 

PAGE 

480. The Problem of Governing 699 

481. Classifications of Governors 699 

482. The Mechanics of the Governor 701 

483. Defects of Governors 704 

484. The Loaded Governor. Porter's Governor 704 

485. The Parabolic Governor 704 

486. Balanced Governor without Spring 705 

487. Balanced or Spring Governors 707 

488. Shaft Governors 709 

489. Inertia Governors 710 

490. Spindle and Shaft-governors Compared 710 

491. Resistance Governors 710 

492. Electromagnetic Governors 712 

493. Dynamometric Governors 713 

494. Safety Stops 713 

495. Marine Engine Governors 714 

496. Connections of the Governor to Control the Engine 716 

PART VI. 

CHAPTER XXXI. 

Engine Auxiliaries. The Condenser and Attachments. ' 

500. Introductory. 717 

501. The Principles of the Steam Condenser 717 

502. The Vacuum Gage 718 

503. The Weight of Injection Water 719 

504. The Volume of the Air Pump 719 

505. The Jet Condenser 720 

506. The Surface Condenser 724 

507. Jet and Surface Condensers Compared 727 

508. The Cold Well. Cooling Towers 728 

509. The Air-Pump and Foot Valve 731 

510. The Wet and Dry Air Pump 732 

511. The Independent Air Pump 734 

51 2. The Circulating Pump 735 

513. The Barometric, Injector, Siphon, or Gravity Condenser 737 

514. The Exhaust-steam Ejector Condenser 739 

515. The Hot Well 740 

516. The Feed Pump. 741 

517. Condensers for Steam Turbines 743 

518. Sundry Special Condensers 743 

519. Concluding Comment 743 



TABLE OF CONTENTS XXV 

CHAPTER XXXII. 
Engine Auxiliaries, Lubricators and Lubrication. 

PAGE 

525. Objects of Lubrication 744 

526. Lubricants, or Lubricating Materials.- : 744 

527.. Tests of Lubricants. 745 

528. Lubrication of Cylinder and Valves 746 

529. Graphite as a Lubricant 748 

530. Lubrication of Bearings 749 

PART VII. 

CHAPTER XXXIII. 

Care and Management. Accidents. 

535. Starting an Engine 753 

536. To Start a Non-condensing Engine 753 

537. To Start a Condensing Engine 754 

538. To Start a Compound Engine 755 

539. To Start a Steam-Turbine 756 

540. Management of Engines 757 

541. Shut-downs in the Engine Room, Major Accidents 757 

542. Minor Accidents or Mishaps in the Engine Room 758 

CHAPTER XXXIV. 
Testing the Power Plant for Economy and Efficiency. 

545. General 760 

546. The Boiler Test. 760 

547. Flue Gases 760 

548. The Calorimeter 761 

549. Report of a Boiler Test : 762 

550. The Engine Test 762 

PART VIII. 

CHAPTER XXXV. 
General Remarks upon the Power Plant. 

555. Concentrated or Subdivided Steam Power 764 

556. Distribution of Power by Electricity, Gas or Air 765 

557. Location of a Power Plant 766 

558. Construction of a Power House 768 

559. Arrangement of the Power Plant 7-69 

560. Fire Protection of the Power Plant 769 

561. Floors of the Power Plant 770 



xxvi TABLE OF CONTENTS 

PART IX. 

APPENDICES. 

PAGE 

565. Historical Summary 771 

566. Steam Tables 773 

567. Table Hjrperbolic Logarithms 778 

568. Historic Illustrations 782 



i 



LIST OF TABLES. 



Table page 

A. Horsepower in Various Units 4 

I. Approximate Water Rates in Steam Engines 14 

II. Ratio of Heating Surface to Grate Surface 17 

III. Relative Evaporation by Some American Coals 17 

IV. Specifications for Boiler Steel 31 

V. Double and Triple-riveted Lap Joints 50 

VI. Double Butt Joints 51 

VII. Fire-Tube Proportions and Arrangement 91 

B. Table of Flue Thicknesses 98 

VIII. Locomotive Boiler Proportions 119 

IX. Calorific Power of Fuels 166 

C. Specific Gravity, Specific Heat and Volume of Gases 169 

D. Table of Chimney Performance 172 

E. Table of Chimney Heights 173 

F. Heat Balance Table 236 

X. Mineral Matter in Solution in Feed Waters 283 

XI. Solubility of Mineral Salts in Hot Water -285 

XII. Coefficients for Resistance in Pipes (D'Arcy) 338 

XIII. Effectiveness of Non-conducting Coverings 361 

XIV. Work per Cubic Foot of Steam with Back-pressure 452 

XV. Steam per Hour and per Horsepower at Different Pressures '. . 453 

XVI. Values of Ratio of Expansion with 100 Pounds Initial 454 

G. Ratios of Cylinder Volumes in Multiple Expansion Engines 470 

XVII. Comparative Installation Costs of Turbine and Engine 539 

XVIII. Charges per Kilowatt Hour for Power Plant Maintenance and Operation. . . 540 

XIX. Value of A c or m as a Fraction of the Work per Stroke 621 

XX. Energy Stored in a Fly-Wheel When Fluctuations are One Per Cent 622 

H. Variation of Lead of Valve in Stephenson Link-Motion 687 



LIST OF ILLUSTRATIONS. 



Fig. page 

1 . Necessary Elements in a Typical Power Plant 5 

2. Analysis of a Complete Power Plant 7 

3. Analysis of Auxiliaries in a Complete Power Plant 8 

4. Piston-Motor Work, and Effort Diagram 11 

5. Convection and Circulation Currents in a Boiler 23 

6. Field Tube for Determinate Circulation 24 

7. Wagon Boiler Section, to Show Absorbing Surface for Heat 25 

8. Fire-Tube and Water-Tube Heating Surfaces, and Effectiveness 25 

9. Shell Stress in a Boiler under Internal Pressure . . . 27 

10. Egg-Ended Cylindrical Boiler 28 

11. Tubular Cylinder Boiler with Five Joints Only 32 

12. Bending Rolls, Horizontal, for Curving Boiler Shell 33 

13. Bending Rolls, Horizontal, Detail of Action 34 

14. Bending Rolls, Horizontal, Detail of Adjustment 34 

15. Shell of Boiler Made of Alternate Cylindrical Rings 35 

16. Flanging Machine for Boiler-Heads. Wood's Hydraulic Type 36 

17. Rivet-Joint in Plate, Showing Flexure at the Lap 39 

18. Punching-Press for Rivet-Holes. Hilles and Jones 40 

19. Punch and Die for Plate-Punching 41 

20. Punch Spiral Type. Kennedy's 41 

21. Half-Blind Hole in Two Lapped Plates 42 

22. Power-Riveting Machine. Steam Driven. Sellers' 44 

23. Power-Riveting Machine. Hydraulic Type. Sellers' 45 

24. Power-Riveting Machine. Pneumatic Lever Type 46 

25. Analytical Treatment of Internal Stress in a Boiler-Shell 47 

26. Bag or Blister from Local Overheating 48 

30. Riveted Joint. Flexure under Stress with Single Cover 50 

31. Riveted Joint. Type Sections 51 

32. Riveted Joint. Lap, Single-Riveted 52 

33. Riveted Joint. Lap, Double-Riveted 52 

34. Riveted Joint. Lap, Triple-Riveted 53 

35. Riveted Joint. Butt, Double-Riveted 53 

36. Riveted Joint. Butt, Triple-Riveted 53 

37. Riveted Joint. Lap with Cover 54 

38. Riveted Joint. Butt with Cover 54 

39. Riveted Joint. Butt, Quadruple-riveted 55 

40. Riveted Joint Showing Methods of Plate Failure 56 

41. Stays, Through Type, in Boiler of U.S.S. Yorktown 59 

42. Stays, Through Type, Detail 59 

43. Stays for Pin-End Type with Sockets 60 

44. Stays, Angle or Tee-Iron Sockets ; 60 

xxix 



XXX LIST OF ILLUSTRATIONS 

Fig. page 

54. Stays, with Radial Tee-Iron Sockets 61 

46. Stays, with Radial Tee-Iron Sockets, Detail 61 

47. Stays, Diagonal, with Flat End and Socket 62 

48. Stays, Diagonal, with Fixed Ends 63 

49. Stays, Diagonal, Forged from Steel Plate 64 

50. Stays, Diagonal, Diagram of Stress in 65 

51. Stays, for Locomotive Crown-Sheets. Baldwin 65 

52. Stays, for Locomotive Crowns and Water Legs. (Belpaire) 66 

53. Stays, for Locomotive Water-Leg, Flexible Type. Tate's 66 

54. Man-Hole Located in Head of Boiler. Lukens 67 

55. Man-Hole Located on Shell with Internal Seating 68 

56. Man-Hole Located on Shell with External Seating 68 

57. Man-Hole with Seating and Cast-iron Lid 69 

58. Man-Hole with Seating and Lid of Steel , 69 

59. Hand-Hole without Seating 70 

60. Edge Planer for Boiler Plate. Hilles and Jones 71 

61 . Calking Diagram for Riveted Joints 71 

65. Dome, Simple Type Form 74 

66. Dome, with Flanged Shell Opening 75 

67. Dome, with Reduced and Reinforced Shell Opening 76 

68. Dome, with Reduced and Reinforced Shell Opening 76 

69. Dome, with Reduced Shell Opening, and Neck- Junction 77 

70. Dome, Replaced by Transverse Pipe 78 

71 . Dry-Pipe for a Marine Boiler 79 

72. Dry-Pipe. Potter Mesh-Separator Type 79 

73. Mud-Drum, Type Form, on Plain Cylinder Boiler •. 80 

74. Mud-Drum, Parallel to the Boiler. HoUey 81 

75. Tubular Boiler. Externally Fired Side Elevation. Hewes and Phillips 85 

76. Tubular Boiler, Externally Fire 1 Front and Cross-Section 86 

77. Tubular Boiler, Pin Drill for Tuoe Sheets 87 

78. Tubular Boiler, Tube Expander 88 

79. Tubular Boiler, Tube Expander 88 

80. Tubular Boiler, Thumb-Swage 88 

81. Tubular Boiler, Section of Expanded Tube 89 

82. Tubular Boiler, Tube-Cutter. Ryerson 90 

83. Tubular Boiler, Ribbed Tube. Serve ; 90 

84. Flue Boiler, Standard Type, Externally Fired. Stanwood 93 

85. Flue Boiler, Two-Flue Type, Externally Fired. Rand 94 

86. Flue Boiler, Bump-Joint for Flue of Medium Size 95 

87. Flue Boiler, Re-Inforcing Ring for Long Flues 95 

88. Flue Boiler, Re-Inforcing Ring with Flanged Sections 96 

89. Flue Boiler, Re-Inforcing Ring. Adamson Type 96 

90. Flue Boiler, Re-Inforcing Ring. Bowling Type 96 

95. Internally-Fired Boiler, Cornish Type 102 

96. Internally-Fired Boiler, Lancashire Type 102 

97. Internally-Fired Double-Furnace Flue. (Strong) 104 

98. Internally-Fired Galloway-Tube Boiler. Sellers 104 

99. Internally-Fired Scotch Marine Boiler, Front View 105 

100. Internally-Fired Scotch Marine Boiler, Perspective 106 

101. Internally-Fired Morrison Corrugated Flue Type 106 



LIST OF ILLUSTRATIONS XXxi 

Fig. page 

102. Internally-Fired Weir's Hydrokineter 107 

103. Internally-Fired Marine Double-Ended 108 

104. Internally-Fired Corrugated Fox or Morrison Flue 108 

105. Internally- Fired for High-Pressure with Combustion Chamber 108 

106., Internally-Fired Flat-Sided Marine Boiler, with Steam Chimney 109 

107. Internally-Fired Flat-Sided Marine Boiler for Ferry-Service. (Orange) 110 

110. Internally-Fired Locomotive, Wagon-Top Type. Baldwin Ill 

111. Internally-Fired Locomotive with Extension Front 113 

112. Internally-Fired Locomotive, Chicago and Alton Type 113 

113. Internally-Fired Locomotive, N.Y. Central Type 114 

114. Internally-Fired Locomotive, Baldwin Locomotive Works 114 

115. Internally-Fired Locomotive, Belpaire Fire-Box. L. and N 115 

116. Internally-Fired Locomotive with Wootton Fire-Box 116 

117. Internally-Fired LoconK)tive Fire-Box over Frames 117 

118. Internally-Fired Locomotive for Stationary Use 117 

119. Internally-Fired Locomotive for A.T. and S.F. with Corrugated Fire-Box .... 118 

120. Internally-Fired Locomotive with Flat Corrugated Fire-Box. Wood 118 

121. Internally-Fired Boiler for Stationary Use without Setting 120 

122. Internally-Fired Boiler for Stationary Use without Setting 121 

123. Internally-Fired Boiler, Robb-Mumford Design 122 

125. Internally-Fired Boiler, Upright Ordinary Type 123 

126. Internally-Fired Boiler, Upright Manning Type 123 

127. Internally-Fired Boiler, Upright Submerged Tube Type 124 

128. Internally-Fired Boiler, Upright Corliss Type 125 

129. Internally-Fired Boiler, Upright Reynolds Type 126 

130. Internally-Fired Boiler, Upright Fire-Engine Type 127 

131. Internally-Fired Boiler, Upright Fire-Engine with Water Tubes 127 

132. Internally-Fired Boiler, Upright Fire-Engine with Field Tubes 128 

134. Externally-Fired Long Cylindrical Elephant Boiler 131 

135. Externally-Fired Long Cylindrical French Boiler. Weimer 131 

136. Externally-Fired Long Cylindrical Durfee Boiler 132 

137. Externally-Fired Long CyUndrical Elephant Boiler. Holley 133 

138. Sectional Boiler, Detail. Harrison- Wharton Type 138 

139. Sectional Boiler, Rust Vertical Straight Tubular 139 

140. Sectional Boiler, Cahall Vertical Straight Tubular 140 

141. Sectional Boiler, Tudor Horizontal Straight Tubular 142 

142. Sectional Boiler, Heine Horizontal Straight Tubular 142 

143. Sectional Boiler, Heine Horizontal Straight Tubular 143 

144. Sectional Boiler, Babcock and Wilcox Inclined Straight Tubular 144 

145-7. Sectional Boiler, Babcock and Wilcox Details 145 

148. Sectional Boiler, Root Type . 146 

149. Sectional Boiler, Root Type, Details 147 

150. Sectional Boiler, Root Type, Details 148 

151. Sectional Boiler, National Tjrpe, Details 148 

152. Sectional Boiler, Worthington Type 150 

153. Sectional Boiler, Stirling or International Vertical 150 

154-5. Sectional Boiler, Thorneycroft Curved Tubular 152 

156-7. Sectional Boiler, Mosher Curved Tubular 152 

158. Sectional Boiler, Allen Inclined Straight Tubular 153 

160. Pipe and Fittings Boiler 156 



xxxii LIST OF ILLUSTRATIONS 



Fig. 



PAGE 

161. Pipe and Fittings Boiler. Almy » » . , o 157 

162. Pipe and Fittings Boiler. Almy ........,.<.,., 158 

163. Coil Boiler, Ward's 159 

164. Coil Boiler. Herreshofif 160 

165. Semi-Flash Boiler. The White Co 162 

166. Chimney Analysis Diagram 168 

167. Chimney Capacity Diagram 173 

168. Boiler Grate- Bars, Cast-iron and Herring-Bone Type 175 

169. Boiler Setting Half Elevation and Section 176 

170. Boiler Grate Shaking, ^tna 177 

171. Boiler Grate Dumping. Lahman-Kirkwood 177 

172. Boiler Grate Shaking and Dumping. McClave 178 

173. Boiler Grate Hollow for Sawdust and Forced Draft 178 

174. Step-Grate for Small Fuel. Roney : 180 

175. Traveling Grate. E. B. Coxe Design 181 

178. Inclined Grates 182 

179. Horizontal Grates 183 

180. Side-Firing System of Firing 184 

181. Coking System of Firing 184 

182. Dead-Plate and Furnace Mouth 185 

183. Ash-Pit Below Floor Level 186 

184. Bridge- Wall, Inverted Arch Form 187 

185. Bridge-Wall, Straight Top Form 188 

186. Boiler Setting with Hollow Side Walls 189 

187. Bridge- Wall Inclined 190 

188. Bridge- Wall Hollow '. . . . 192 

189. Combustion Chamber for Long Boiler ; 193 

190. Back-Connection, Arch Bar 194 

191. Back-Connection, Suspended 194 

192. Front-Connection to Flue 196 

193. Boiler-Setting Showing Overhead Flue 197 

194. Damper Regulator by Steam Pressure Direct 198 

195. Damper Regulator Locke Hydraulic Type 199 

196. Chimney Construction Types 203 

197. Forced Draft, Marine System 204 

198. Forced Draft, Marine System of U.S.S. Swatara 205 

199. Forced Draft with Preheater 207 

200. Forced Draft American Line Pier 207 

201. Forced Draft Introduced into Ash-pit 208 

202. Hawley Down-Draft Furnace 210 

203. Down-draft Furnace in Internally Fired Boiler 211 

204. Dutch-Oven Type of Furnace 212 

205. Smoke-Chart by Ringelmann 214 

206. Smoke-Standard by Breckenridge 215 

207. Boiler-Setting, Externally-fired Tubular Boiler , 216 

208. Boiler-Setting, Externally-Fired Tubular Boiler 218 

209. Boiler-Setting Steel Lug to Carry Weight 219 

210. Boiler Setting Steel lug for Hanging Weight 219 

211. Boiler-Setting Steel eye for Hanging Weight 219 

212. Boiler-setting, steel eye for hanging Weight „ 220 



LIST OF LLUSTRATIONS xxxiii 

Fig. ^ PAGE 

213. Boiler-Setting, full Front, Half Flue Doors 221 

214. Boiler-Setting, Full Front, Full Flue Doors 222 

215. Boiler-Setting, Half-Front Perspective Section 223 

216. Boiler-Setting, Gallows Frame 225 

217. Oil and Gas Firing, Argand Principle 227 

218. Oil Firing with Steam Injector, Hayes 229 

219. Oil Firing with Air Injector, Grundell-Tucker 229 

220. Oil Firing with both Steam and Air Injection, Reid 229 

221. Oil Firing with atomizing of Oil, Korting 229 

222. Oil Firing for Locomotives, Urquhart 230 

223. Oil Firing Furnace Arrangement 230 

224. Oil Firing Plant Arrangement 231 

225. Saw-Dust Firing 235 

226. Bagasse Burning Furnace 236 

230. Boiler Feed-pump, Belt or Motor Driven 242 

231. Boiler Feed-Pump, Plunger-Type, Double-Acting 244 

232. Boiler Feed-Pump, Plunger-Type, Double-Acting 244 

233. Boiler Feed-Pump, Fly- Wheel Type with Yoke, Clayton 245 

234. Boiler Feed-Pump, Fly- Wheel Type with Connecting Rod 245 

235. Boiler Feed-Pump Direct-Acting Type 246 

236. Boiler Feed-Pump, Duplex Type Section, Worthington 247 

237. Boiler Feed-Pipe, Closed by Scale 249 

238-9. Boiler Feed-Pipe, Check- Valves 251 

240. Boiler Feed-Injector, Type-Section , 254 

241. Boiler Feed-Injector, Sellers, Lever Type 259 

242^. Boiler Feed-Injector, Korting Double Tube Type 259 

243. Boiler Water-Gage-Glass Tube, Simple 262 

244. Boiler Water-Gage Column-Pipe Fixture 262 

245. Boiler Water-Gage Glass with Safety-Fixture 263 

246-7. Boiler Water-Gage Glass with Safety-Fixture 264 

248. Boiler Water-Gage Glass Klinger Type 265 

249-50. Boiler Water-Gage Cocks, Special Forms 267 

251. Boiler Water Level Float Alarm 268 

252. Fusible Plug 269 

253. Steam-Pressure Gage, Diafram Type 272 

254. Steam-Pressure Gage, Bourdon Spring-Tube Type , 273 

255. Steam-Pressure Gage, Bourdon with Lane's Improvement 273 

256. Steam-Pressure Gage, siphon Pipe 274 

257. Safety-Valve, Lever Type 276 

258. Safety-Valve, Pop-Type 277 

259A. Historic Watt- Wagon Boiler, Showing Automatic Feed of Fuel and Water . . . 782 

260. Flue-Cleansing Scrapers and Brush 281 

261. Flue-Cleansing Jet Apparatus for Steam 282 

262. Surface blow-off Apparatus 287 

263. Flue or Tube Cleansing Impact Motor-Driven Apparatus 288 

264. Flue or Tube Cleansing Impact Motor-Driven Apparatus 289 

265. Feed- Water Heater, Open type, Lime-Catcher, Hoppes 289 

266. Feed- Water Filter, Alternate Pressure Type 290 

267. Feed-water Filter Reversing Current Type 291 

268-9. Boiler-Plate Corroded by Grooving ; . . . 293 



xxxiv LIST OF ILLUSTRATIONS 

Fig. , PAGE 

270. Vaporization Diagram to Show Stored Energy 302 

271. Mechanical Stoker, with TraveHng Grate (B. & W) 310 

272. Mechanical Stoker, with Reciprocating Bar (Wilkinson) 311 

273. Mechanical Stoker, with Tilting Step-Grate (Roney) ... " 312 

274. Mechanical Stoker, with Underfeed. J.ones, American 313 

275. Mechanical Stoker, with Caldwell Mechanical Shovel ... 314 

276. Feed-Water Heater. Economizer Type. Scheme Plan 316 

277. Feed- Water Heater, Economizer Type, Detail 317 

278. Feed-Water Heater, Economizer Type, Perspective '. 318 

279. Feed- Water Heater, Exhaust-Steam Open Heater Type 320 

280. Feed-Water Heater, Exhaust-Steam 321 

281. Feed- Water Heater, Exhaust Steam, Closed Heater Type 322 

282. Feed- Water Heater Exhaust-Steam Closed Type 323 

283. Feed- Water Heater Exhaust-Steam Closed Type 324 

284. Feed- water Heater, Exhaust-Steam Closed Type 325 

285. Superheating Apparatus, Foster B. & W 326 

286. Superheating Apparatus, Foster Direct 327 

287. Superheating Apparatus, Cole Locomotive 328 

290. Combustion Recorder, Sarco System 331 

291. Steam-Piping, Steel Riveted 339 

292. Steam-Piping, Joint with Screwed Union 341 

293. Steam-Piping, Joint with Screwed Flange 341 

294. Steam-Piping, Joint Gasket 342 

295. Steam-Piping, Joint Metal Ring and Ground Face 342 

296. Steam-Piping, Joint Modified Screwed Flange . . 342 

297 Steam-Piping, Joint Modified Screwed Flange 342 

298. Steam-Piping, Joint Loose Flange, American •. "343 

299. Steam-Piping, Joint Loose Flange, British 343 

300. Steam-Piping, Joint Welded Flange 343 

30L Steam-Piping, Joint Van Stone Flange 344 

302. Steam-Piping, Joint with Welded Nozzle Outlets 344 

303. Steam-Piping, Joint Fittings ^ 345 

304. Steam-Piping, Expansion Loop 345 

305. Steam-Piping, Expansion by Offsets 346 

306. Steam-Piping, Expansion by Slip Joint 346 

307. Steam-Piping, Expansion by Balanced Slip- Joint 347 

308. Steam-Piping, Expansion by Corrugated Nipple 347 

309. Steam-Piping, Expansion by Disks 348 

310 Steam-Piping, Hanging by Rollers and Suspensions 349 

311. Steam-Piping, Hanging by Rollers and Brackets 349 

312 Valve for Pipe, Globe Type .' 350 

313. Valve for Pipe, Globe Type, Vertical on Horizontal Run 350 

314. Valve for Pipe, Angle Type 350 

315. Valve for Pipe, Gate Type Advancing Stem 351 

316. Valve for Pipe, Gate Type Non- Advancing Stem 351 

317. Valve for Pipe, Gate Type Smaller Sizes 352 

318. Valve for Pipe, Gate Type with B5^-pass 352 

320. Steam-Piping with Side Branch Outlet : 354 

321. Steam-Piping Drainage Trap Bucket Type, Nason 355 

322. Steam-Piping Drainage Trap Float Type 356 



LIST OF ILLUSTRATIONS xxxv 

Fig. page 

323. Steam Piping Drainage Trap Counterpoise Type 356 

324. Steam-Piping Drainage by Pocket 357 

325 Steam-Piping Drainage by Separator, Strattou 357 

326 Steam-Piping Drainage by Separator, Sweet 357 

327. Steam-Piping, Drainage by Separator Goubert 357 

328. Steam-Piping Drainage by Separator •. 358 

329. Steam-Piping Drainage by Separator 358 

330. Steam-Piping Drainage by Steam-loop 359 

331 . Steam-Piping Exhaust Spiral Riveted Type 362 

332. Oil-Separators 363 

333. Oil-Separators 364 

334. Oil-Separators 364 

335. Oil-Separators 364 

336. Oil-Separators Edmiston Filter . . 365 

337. Exhaust Heads 366 

338. Exhaust Heads : 367 

339. Back-Pressure Valves 368 

340. Reducing Valves ' 369 

345. Steam Engine, Typical Form and Mechanism. Atlas 373 

346. Steam Engine, Typical Form and Mechanism. Hunt 374 

347-8. Steam Engine, Mechanism as a 4-Bar Linkage 377 

349-50. Steam Engine, Mechanism as a 4-Bar Linkage 377 

351. Steam Engine, Mechanism Trunk-Type. 378 

352-3. Steam Engine, Mechanism Oscillating-Type, Case . . .• 379 

354. Steam Engine, Mechanism Oscillating-Type, Marine 380 

355A. Steam Engine, Mechanism Trunk-Type, H. M. S. Bellerophon 783 

356. Steam Engine, Mechanism Trunk-Type, Westinghouse 381 

357 A. Steam Engine, Mechanism Trunk-Type, for Derrick ; 784 

358 A. Steam Engine, Mechanism Trunk-Type. Earle C. Bacon 784 

359 A. Steam Engine, Mechanism Back-Acting of. S. S. Belle 785 

360 A. Steam Engine, Mechanism Back-Acting of. H. M. S. Agincourt 786 

361. Steam Engine, Mechanism Back-Acting Blowing Engine 382 

362. Steam Engine, Mechanism Back-Acting Compressor 384 

365. Kinematic Diagram of Steam Engine Mechanism 385 

366. Kinematic Diagram of Steam Engine Mechanism 385 

367. Kinematic Diagram of Steam Engine Mechanism 387 

368. Kinematic Diagram of Steam Engine Mechanism 387 

369. Kinematic Diagram of Steam Engine Mechanism 389 

370. Kinematic Diagram of Steam Engine Mechanism 393 

371. Kinematic Diagram of Steam Engine Mechanism 394 

372-3. Kinematic Diagram of Steam Engine Mechanism 396 

374. Net Impelling Effort Diagram for Crank-Pin 398 

375. Net Turning Effort Diagram for Torque ' 399 

376. Flinging Stress Diagram for Connecting-Rod 401 

377. Accelerating Effort Diagram for Short Connecting-Rod 402 

378. Accelerating Effort Diagram for Short Connecting-R-^ i 403 

380. Vertical Engine, Cross-Compound, Inverted. Mclntosh-Seymour 407 

381. Vertical Engine, Triple Marine, Inverted . . ._ 408 

382. Vertical Engine, Pumping, Inverted. Reynolds-Allis 410 

383 A. Vertical Engine, Pumping, Direct. Holly Mfg. Co 787 



XXXVl LIST OF ILLUSTRATIONS 

Fig- page 

384. Inclined Engine. L. C. and D. Channel Steamer , -411 

385. Inclined Engine, Pumping. Holly Mfg. Co ,.,...= 412 

386. Inclined Engine, Sound Steamer, and H. R. L 413 

387. Horizontal Vertical Engine. Buckeye 414 

388. Horizontal Vertical Compressor. Frick Eng'g. Co 415 

389. Beam Engine. Hudson River Paddle Wheel Practice 418 

390. Beam Engine U. S. Cruiser Chicago, Coryell. 419 

391. Beam Engine, Lawrence Water Works. Leavitt 420 

392. Beam Engine, N.Y. Water Works. Gaskill 421 

393. Beam Engine, Pumping, Dean Co . , . . 423 

394. Beam Engine, Pumping, Dean Co 424 

395. Beam Engine, Corliss Pawtucket Pumping 425 

396 A. Half-Beam Engine, U.S. Monitor. Monadnock . 788 

397 A. Side-Lever Engine of U.S. Pacific 789 

400. Cornish Engine, Beam Type, Cylinder Section 430 

401. Cornish Engine, Cataract 430 

402 A. Cornish Engine, Brooklyn Water Works. Follows 489 

403. Single Acting Engine, Trunk-Type. Westinghouse 433 

404. Single Acting Engine, Trunk-Type. Westinghouse 434 

405. Single Acting Engine, Trunk-Type. Willans 435 

406. Right-Hand and Left-Hand Engine 437 

407. Throw-Over and Throw-Under Engine, Belt Forward or Back 437 

408. Center-Crank Engine, Front View. Ames . . 439 

409. Three-Cylinder Single or Double Acting Engine. Brotherhood 440 

410. Steam Engine Indicator 443 

411. Steam Engine Indicator Diagram without Expansion ., 444 

412. Steam Engine Indicator Diagram with Expansion 446 

413. Steam Engine Indicator Diagram with Too-Early Cut-Off 449 

415. Steam Engine Indicator Diagram with Throttling Governing 450 

416. Steam Engine Indicator Diagram with Variable Admission 457 

417. Steam Engine Indicator Diagram Throttling and Cut-Off Compared- 458 

418. Steam Engine Indicator Diagram of Ideal Condensing Engine 461 

419. Steam Engine Indicator Diagram of Condensing and Non-Condensing Com- 

pared 462 

420. Steam Engine Indicator Diagram Ideal for Computing Mean Pressure ....... 466 

425. Steam Engine Indicator Diagram for Compound Engine 468 

426. Steam Engine Indicator Diagram for Triple-Expahsion Engine 468 

430. Compound Engine. Horizontal Tandem Type. Ideal 476 

431. Compound Engine. Vertical Tandem or Steeple Type. Porter 477 

432. Compound Engine. Horizontal Tandem Type. Ball- Wood 479 

433. Compound Engine. Horizontal Tandem Type. Ames 480 

434. Compound Engine. Horizontal Tandem Pumping Type. Worthington 481 

435. Compound Engine. Beam Vertical Type. GrafT, Phila. W.W 482 

436. Compound Engine. Vertical Side-by-Side Type. Bates 483 

437. Compound Engine. Vertical Side-by-Side Type. Reeves 484 

438. Cross-Compound Engine. Allis-Chalmers 486 

439. Triple-Expansion Engines, Marine Type, Cylinder Grouping 487 

440. Quadruple-Expansion Engines, Marine Type, Cylinder Grouping 488 

441. Reheater for Triple Engine 491 

442. Indicator Diagram of Woolf Compound Engine 492 



LIST OF ILLUSTRATIONS XXXvii 

Fig. page 

443. Indicator Diagram of Woolf Compound Engine c c . . . . 492 

444. Indicator Diagram of Woolf Compound Engine ...... o...,« o.. , 493 

445. Indicator Diagram of Woolf Compound Engine 493 

446. Indicator Diagram of Cross Compound Engine, Reduced 494 

450. Rotary Engine Section Diagram 498 

451. Rotary Engine Section Diagram ... 498 

452. Rotary Engine Section Diagram 499 

453. Rotary Engine Section Diagram 499 

454. Rotary Engine Section Chamber Wheel Gear 499 

455. Rotary Engine Section Alternating Piston and Abutment 500 

456. Rotary Engine Section Embodying 452. Lidgerwood . . 501 

457 A. Ericsson's Vibrating-Piston Engine 789 

460-1. Steam Turbines, Historic Forms ■ 506 

462. Steam Turbines, Work Diagram in Expanding „ 509 

463. Steam Turbines, De Laval Nozzle . 512 

464. Steam Turbines, De Laval Diagram * 512 

465. Steam Turbines, De Laval with Multiple Nozzles 513 

466. Steam Turbines, Reaction Type without Impulse. Dow's 514 

467. Steam Turbines, Kerr Multicellular Type 515 

468. Steam Turbines, Kerr Multicellular Type 515 

469. Steam Turbines, Kerr Multicellular Type *. 516 

470. Steam Turbines, Terry Type 517 

471. Steam Turbine^ Parsons- Westinghouse Type 520 

472. Steam Turbines, Parsons- Westinghouse Governor Detail 521 

473. Steam Turbines, Parsons- Westinghouse 522 

474. Steam Turbines, Parsons- Allis-Chalmers 523 

475. Steam Turbines, Parsons- Allis-Chalmers 524 

476. Steam Turbines, Parsons-AUis-Chalmers Detail 524 

477. Steam Turbines, Curtis Blading 525 

478. Steam Turbines, Curtis Vertical Type 526 

479. Steam Turbines, Curtis Vertical Detail of Stages 528 

480. Steam Turbines, Curtis Vertical Footstep Detail 529 

481. Steam Turbines, Parson's Marine on S.S. Mauretania 531 

482. Steam Turbines, Parson's Marine for Warship Conditions 532 

483. Steam Turbines, Curtis Marine for Warship Conditions 533 

484. Steam Turbines, Bulk Contrasted with^ross-Compound 536 

485. Steam Turbines, Bulk Contrasted with Angle-Reciprocating 536 

486. Steam Turbines, Performance Plotted , 541 

487. Steam Turbines, Performance Plotted 542 

490. Balanced Engine, Wells Type 548 

491. Engine Foundation 551 

492. Engine Foundation with Template 553 

493. Engine Foundation with Template 553 

494. Engine Foundation with Bed in Place and Shimmed 556 

495. Outboard Bearing for Shaft with horizontal and Vertical Adjustment 559 

496. Bed-Plate Ribbed Box Pattern with Surbase 561 

497. Bed-plate Porter or Tangye Standard Type 562 

498. Bed-Plate Porter or Tangye Semi-Enclosed, Russell 563 

499. Bed-Plate with Supported Cylinder, Russell 564 

500. Bed-Plate Corliss Type with Foot ... 565 



XXXVlll LIST OF ILLUSTRATIONS 

% 

Fig. page 

501 . Bed-Plate Corliss Type Section of Girder .............. , . . , . 566 

502. Bed-Plate Tangye Type with Foot, Bates ..... , 567 

503. Bed-Plate Tangye Type with Open Guides, Mclntosh-Seymour ............ 570 

504. Bed-Plate Allis-Chalmers Corliss Cross-Compound , 570 

505. Bed-Plate Buckeye-Tandem Compound 571 

506. Bed-Plate Straight Line Engine, Sweet 572 

507 A. Bed-Plate Box or Tank Type, Watertown Engine 790 

510. Cylinder Section, to Show Counterbore and Piston, Valves A and S Type .... 573 

511. Cylinder Relief Valves for Condensed Water 575 

512. Cylinder Jacket Joints, Leavitt and Corliss 576 

513. Piston, Box Type 578 

514. Piston, Follower Type, Baldwin Locomotive 579 

515. Piston, Plate Type 579 

516. Piston, Packing-Ring Detail 582 

517. Piston, Packing-Ring Adjustment, Durfee 583 

518. Piston, Packing-Ring set out by Steam 587 

519. StufRng-Box, with Metallic Packing 588 

520. Stuffing-Box, with Metallic Packing 589 

521. Stuffing-Box, with Metallic Packing. 590 

525. Cross-Head Guides — Single Type 593 

526. Cross-Head Guides for Slipper Type 594 

527. Cross-Head for Flat Guides 595 

528. Cross-Head Cylindrical Guides 596 

529. Cross-Head Angular or Trough Guides, Bates 596 

530. Cross-Head for Four Flat Guides 598 

531. Cross-Head for Vertical Cylindrical Guides, Atlas , 598 

532. Connecting-Rod, Wedge and Gib and Cotter Brasses 601 

533. Connecting-Rod, Stub-Ends 602 

534. Connecting-Rod of I-Section 603 

535. Connecting-Rod, Marine Type with Bolts 604 

536A. Connecting-Rod, C. W. Hunt Steel Ball Adjustment 791 

537. Connecting-Rod, Solid End Types 605 

540. Crank-Shaft for Cross-Compound Side-Crank Types 607 

541 . Crank-Shaft for Triple Double-Crank Type 607 

542. Crank for Side Crank Type, Unbalanced 609 

543. Crank with Counterweight Double . . . . • . ', 610 

544 A. Crank Double, with Detachable Counterweight, Skinner . , 793 

545. Crank Double, for Marine Inverted Vertical Engine 610 

546. Shaft, Marine Propeller Type 612 

547. Shaft, Marine Propeller Type , . . 613 

548. Shaft Bearing, Showmg Quarter Boxes, Bates 614 

549. Shaft Bearing, Rus.sell 615 

550. Eccentric Disk in Two Halves 616 

551. Eccentric Strap _ 617 

552. Fly-wheel Effort ReceiA ed from Crank-Pin per Stroke 620 

553. Fly-wheel of Cast Iron in Two Segments 624 

554. Fly-wheel of Cast Iron in Several Segments, Boston Sewage ...,,. 624 

555. Fly-wheel Joint by H. V. Haight 625 

560. Poppet-Valves, Type Forms 629 

561. Poppet-Valves Balanced, River-Boat Engine Type ' 630 




LIST OF ILLUSTRATIONS xxxix 

Fig. , PAGE 

562. Four- Valve Engine Cylinder Section 632 

563. Four-Valve Engine Cylinder Section 632 

564-5. Plug-valve, Three-Way Type 634 

566-7. Plug- Valve, Four- Way Type 635 

568-9.. Slide-Valve, Sections 636 

570. Crank Becomes an Eccentric 638 

571 . Trammel to Use in Setting Valves * 639 

572. Slide-Valve — B Section '. . . 640 

573. Slide-Valve with Inside and Outside Lap 641 

574. Slide-Valve with pre-opened Exhaust Port 641 

575. Slide-Valve to Show I>ead 644 

576. Setting of Valve by Trammel, Fig. 571 645 

577A. Forney's Mechanism for Drawing Motion Curves of Valves 791 

578A-9A. Valve Motion Curves 792 

580. Zeuner Analysis for Valve-Motion Diagram 647 

581. Zeuner Analysis for Valve-Motion Diagram 649 

582. Zeuner Graphic Diagram for Valve Setting and Design 649 

583. Zeuner Graphic Diagram for Valve Setting and Design 649 

584. Zeuner Graphic Diagram for Valve Setting and Design 650 

585. Zeuner Graphic Diagram for Design and Setting 651 

586. Zeuner Graphic Diagram for Valve Design and Setting 653 

587. Zeuner Graphic Diagram for Valve Design and Setting 653 

588. Meyer-Riding Cut-off Valve Section 655 

589. Cut-off Valve in Separate Steam-Chest 655 

510. Cut-off Valve Separated from Exhaust, Porter-Allen 656 

591 . Short-ported Cylinder Section 658 

592. Short-ported Cylinder Section, Buckeye 659 

593. Allen Hollow-Shell Valve and Double-port Effect 660 

595. Gridiron Slide Valve Principle 660 

596. Gridiron Slide Valve of Mcintosh Seymour Engino 660 

597. Gridiron Slide Valve of Worthington Direct-Acting Pumjo 661 

598A. Pressure Plate Design of Woodbury Engine 794 

599. Pressure Plate for Relief of Pressure 663 

600. Balanced Valve. Piston Type. Reeves 664 

601. Balanced Valve. Piston Type 665 

602. Balanced Valve. Pressure-plate Type. Atlas 666 

603. Balanced Valve. Pressure-plate Type. Richardson 666 

604. Balanced Valve. Pressure-plate Type. Porter-Allen 667 

605. Balanced Valve. Pressure-plate Type. Sweet 668 

606. Balanced Valve. Pressure-plate Type. Flexible 669 

607. Balanced Valve. Taking Steam Internally. Giddings 669 

608. Cam-operated Valve Gear. Double-outside Cam 670 

609-10. Cam-operated Valve Gear of Western River Boat 671 

611-12. Cam-operated Valve Gear. Details 673 

613. Cam-operated Valve Gear with Air-spring Return 674 

614. Cam-operated Valve Gear of Western River Boat 675 

615. Trip-release Valve Gear of Greene Engines 676 

616. Corliss Valves and Cylinder , 677 

617. Corliss Valves with Wrist-plat(> , 677 

618. Corliss Valves with Wrist-plate 678 



xl LIST OF ILLUSTRATIONS 

Fig. page 

619. Corliss Valves. Release and Governor Gear 680 

620. Gab-hook for Valve releasing Gear 683 

621 . V-gab Hook for Valve-releasing Gear 683 

622. Stephenson Reversing Link-motion for Locomotives 685 

623. Stephenson Reversing Link-motion for Locomotives 686 

624. Gooch Reversing Link-motion for Locomotives 688 

625. Joy Reversing Link-motion for Locomotives 689 

626-7. Joy Reversing Link-motion for Locomotives 690 

628. Walschaert Reversing Link-motion for Locomotives 691 

629. Walschaert Reversing Link-motion for Vauclain-Baldwin Type 692 

630. Allen-Fink Reversing Link-motion 693 

631. Meyer Valve-gear derived from Fig. 588 697 

632. Riding Cut-off with Trapezoidal Ports 698 

633. Riding Cut-off. Rider's Design 698 

634. Balanced Slide Valve with Cut-off below Valve . 698 

635A. Corliss Engine. Old Fishkill Landing Type 795 

640-1. Governors. Diagram of Fly-ball Types 701 

642. Governors, Diagram of Wilson-Hartnell Type 703 

643. Governors, Diagram of crossed-arm Type 705 

644. Governors, loaded crossed-arm Type (Steinlen) . 705 

645. Governors, loaded crossed-arm Type (Buss) 706 

646. Governors, balanced Babcock and Wilcox Type 706 

647. Governors, Pickering Spring 707 

648. Governors, Waters' Spring 707 

649. Governors, Wright, Gardner, Spring 708 

650. Governors, Shaft Type. Rites' Ideal ' 708 

651 . Governors, Inertia Type 709 

652. Governors, Inertia Type 711 

653A. Governors, Shaft Type. Westinghouse 796 

654A. Governor, Porter loaded type on Twiss Engine 797 

655. Governors, Resistance Type 712 

656. Engine-stop. Locke-system 715 

657. Marine Pendulum Governor 716 

660. Condenser, Jet- type of River-boat Practice 720 

661. Condenser, Jet-type with Pump 721 

662. Condenser, Jet-type with Centrifugal Pump. Alberger 722 

663. Condenser, Jet and Surface combined in one Plant 723 

664. Condenser, Surface, with attached Air-pump 724 

665. Condenser surface, Wheeler Type 725 

666A. Condenser, Surface Types of Tube Joints 798 

667. Condenser Alberger 727 

668. Air-Pump with Jet Condenser 728 

669. Cooling Tower, for Injection Water 729 

670. Cooling Tower, for Injection W^ater 730 

671. Air-Pump, combined Wet and Dry. Edwarde's 733 

672. Air-pump, Independent, with Circulating Pump •. 735 

673. Barometric Condenser 736 

674. Barometric Condenser Head 737 

675. Condenser, Jet with Pump and Break- vacuum Float 738 

675A. Pump Condenser Craig's with Float Adjustment 799 



LIST OF ILLUSTRATIONS xli 

Fig. page 

676. Exhaust steam Jet Flow Condenser. Morton's 739 

677. Exhaust-steam Jet flow Condenser. Schutte 740 

678 A. Exhaust Steam Jet flow Condenser. Schutte 799 

679. Exhaust-steam Jet Flow Condenser. Schutte 741 

680. Turbine Condensing Auxiharies. Worthington 742 

685. Lubricator Positive or Precision by Pump 746 

686. Lubricator by Head of Condensed Steam 747 

687. Lubricator Sight-feed Type 748 

688-9. Lubricator attached to Engine, for Crank-pin 749 

690. Lubricater for grease 751 

691. Manhattan Elevated Ry. Power House, New York City, follows 768 

692. Metropolitan Street Ry. Power House, New York City, follows 768 

695 A. Square-piston, or double Chamber Engine. Dake 800 

696A. Colt-Disk or 6-cylinder Engine 800 

697A. Babcock and Wilcox Steam-thrown cut-off Valve 800 



THE MECHANICAL ENGINEERING 
OF STEAM POWER PLANTS. 



PART I. INTEODUCTOEY. 



1. The Function of the Power Plant. A power plant is an instal- 
lation of the necessary devices and machinery to make available 
a supply of mechanical energy or to generate or liberate such energy 
from the material in which it is stored. Such installation will cost 
money, and the necessary capital will, therefore, be invested or planted 
at the selected point with a view to a financial return from the sale of 
the power. In some cases the owner of the power plant and the con- 
suming user of its product are the same parties; in others^ the power 
is sold outside to others. The accounting or financing should be able 
in either case to give the exact cost of the unit of power to the producer 
in dollars per year, that the plant may be self-supporting and yield a 
profit on the capital invested. Hence the function of the power 
plant is to furnish the maximum power at the least cost, such cost 
being made up of the elements of interest on the investment, depre- 
ciation, and maintenance, together with the aggregate of the operating 
expenses properly so called. 

There will therefore be usually two differing standards to be borne ill 
mind. One is that where the first or investment and the up-keep costs 
are to be kept low, with a view to short hfe of the plant and its sale at a 
sacrifice when its function is discharged. The other is the larger and 
more permanent plant, with an expected longer or perhaps continuous 
hfe during the existence of the same industrial or civic conditions. In 
the former the first cost is less regarded because usually smaller in 
amount: in the latter, large investment is justifiable to save fuel expense 
and diminish the repair and maintenance expenditure to keep the plant 
in prime condition for economic production of power. Solutions of 

1 



2 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

engineering problems in the power plant have, therefore, always the 
financial factors present in them, since nearly every technical difficulty 
can be overcome if it is worth the cost in dollars to solve it. 

2, Sources of Motor Energy for the Power Plant. Internal and 
External Combustion. In a broad and general view of power generation 
there are three origins for such power. (1) Muscular force of men or 
animals; (2) Forces resulting from chemical combinations, giving heat 
or electrical energy; (3) Gravity, or the force by which the earth draws 
toward its center the masses which are capable of such motion. It will 
be obvious that the Hmitations on muscular force imposed by 
the vital energies both in extent and continuity preclude anything 
like large installations dependent on it: and the expense of gener- 
ating electric energy from battery reactions is equally conclusive. 
Gravity and heat energy from fuel are the two practical sources of 
power. 

To utilize gravity as a source of motive power, masses must be lifted 
away from the center of the earth and then be allowed to descend 
towards it, doing work in such descent. The only usable masses which 
are lifted by natural forces and without expenditure of costly power are 
those of the water and air which are raised by the heat of the sun to the 
upper levels of the atmosphere. The descent of the colder air in adjust- 
ment of barometric pressures causes the winds which are used in air 
motors such as wind-mills; but the small power and lack of continuity of 
their motion restricts them to special classes of service, such as pumping 
or intermittent electric generation where storage devices can be made 
available. With water-power utilization, there must be high land or 
mountains available, upon which the water may fall and be accumulated 
in water-courses, natural or artificial, and be led in quantities to the 
motor to be driven. Where such elevations are not available, and the 
head of water is only that of slow moving streams, the motor becomes of 
inconvenient size and cost. Hence the fiberation of heat energy from 
fuel is the most important and generally significant of all the systems of 
manufacturing mechanical energy. 

This fiberation of stored energy from a fuel in the form of heat, and its 
transformation by natural law into mechanical energy may be done in 
two general ways, or by the use of two media. In either system, the 
fuel must be burned or oxidized. This means a chemical union of its 
heat-producing elements with the oxygen of the air in proper propor- 
tions, so that the heat may be released or made available in that 
chemical process. The research of Joule showed that such release of 
heat gives 778 foot-pounds of work for each unit of heat available in 
the fuel if the transformation into mechanical energy is complete. This 



INTRODUCTORY 3 

released heat may be used in the one system to heat the air which 
supports its combustion within the space enclosed behind a piston in a 
cyhnder and by means of the pressure resulting in that air from its 
effort to expand by heat, the effort is exerted upon the piston. Such 
motors as operate with heated air upon this system are called internal 
combustion motors. The fuel may come into the cylinder in the form 
of gas or liquid, and the engine will be called a gas engine, or a kerosene, 
or gasohne, or alcohol engine. Power plants working upon this system 
form a class by themselves and have been elsewhere treated by the 
author.* The second system causes the heat of the combustion to 
impart pressure to a medium contained within an enclosed vessel to 
which the heat-source is external. The pressure resulting in the vessel 
from the expansion of the medium by heat is led to a cyUnder within 
which is a piston, or is exerted by the living force due to its velocity 
against vanes, doing work as in the first case. This is called the 
external combustion system, and steam or the vapor of water is 
the most convenient and accessible medium. It costs nothing but 
the interest on the investment to bring the water in, or the water-tax 
to the municipality to compensate the latter for its expenditure for the 
same object. Other media such as ammonia compounds, ethers, alco- 
hols and petroleum derivatives have been proposed in order to avail of 
their greater volatility, and to escape the objections to water from its 
high pressures with low temperature and its readiness to condense in the 
motor cylinder and in the piping. This again is offset by the high 
specific heat of water and the fact that for this reason a given cylinder 
v©lume brings in more heat than with a less dense medium; or a smaller 
cyhnder with steam does the same work as a larger one supphed with 
a more volatile medium. | This treatise concerns itself, therefore, only 
with the external combustion system and the steam engine and boiler 
as means to carry it out in practice. 

3. Measurements of the Work Unit of Output. Indicated Horsepower. 
Brake Horsepower. When the steam engine replaced the horse motor 
it was convenient to standardize the new power in terms of the old. 
James Watt established by experiment with powerful British or Nor- 
man draft horses that their capacity was a work of 33,000 foot-pounds 
per minute. In other units than the foot and the pound its equivalents 
are: 

* The Gas Engine, a treatise on the Internal Combustion Engine using gas, 
gasoline, kerosene, alcohol, or other hydro-carbon as source of energy. 

t See Heat and Heat Engines, by F. R. Hutton, Chapters on Vapors as Heat Car- 
riers and Vapor Engines. John Wiley & Sons. 



MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



Horsepower. 


English. 

Foot-pounds per 

Minute. 


French. 

Kilogrammeter per 

Minute. 


Austrian. 

Foot-pounds im 

Minute. 


English and American 
French 


33,000 

32,470.4 

33,034.2 


4,572.9 

4,500 

4,549.5 


25,774 
24 561 


Austrian 


25' 800 



The English horsepower is 1.0163 force de cheval. 

The French force de cheval is 0.95363 English horsepower. 



If the power is to be transmitted in the form of electrical energy over 
wires the unit is the kilowatt, which is energy at the rate of 1000 joules 
per second, the joule being the energy expended by the international 
ampere against an international ohm. The watt is equivalent to y^^ of 
a horsepower, or the kilowatt per hour is equivalent to 1.34 horse- 
power per hour. 

Brake horsepower, or effective horsepower, is the net work in foot- 
pounds or other units delivered Trom the engine or motor after all losses 
from its own friction have been deducted. It is measured by a brake or 
power absorbing or measuring device and is, therefore, also called dyna- 
mometer horsepower or net horsepower. 

Indicated horsepower is the capacity of the engine measured at the 
cylinder by an instrument devised by James Watt which he called the 
indicator. This is an apparatus in which a piston of known area receives 
the pressure of the steam at the same time as the engine piston. Its 
motion is opposed by a calibrated spring which is compressed or extended 
proportionately to the pressure. If the end of the rod attached to the 
piston and resisting spring is fitted with a pencil or tracing point, it can 
be made to indicate at every point in the traverse of the engine piston 
the pressure which was acting on it : a mean of these pressure ordinates 
upon a traced diagram will give the mean pressure, which, multiphed 
into the area of the engine piston, and by the feet traversed in the 
minute of time will give the horsepower supplied to the cylinder in that 
time. This mean pressure can also be mathematically computed from 
formulae of sufficient accuracy. 

The Nominal Horsepower is an old term now properly disused, which 
was based on an untenable assumption that all engines of a given diam- 
eter and stroke (or cylinder volume) Were of the same horsepower, 
whatever the mean pressure on the piston or the speed of its traverse 

4. Elements and Analysis of the Steam Power Plant. The simplest 
possible case of a power plant reduced to its lowest terms must include a 
grate to burn coal and a chimney to make draft and carry off smoke 



INTRODUCTORY 



and burnt gases. In con- 
tact with the heat of this 
fire and its hot gases there 
must be a metalUc vessel 
to hold water to be boiled 
and -made into steam. 
The vessel must be strong 
enough to resist the pres- 
sure. There must be a 
pump to force water into 
this boiler against the 
pressure, and a pipe with 
a valve in it to carry 
steam over to the engine. 
There must be the engine, 
gt whose revolving shaft 
the continuous effort 
appears in available form 
to do work. Referring to 
the diagram sketch of 
Fig. 1 and the analysis 
of Fig. 2, the coal from 
the pile, No. 2 and 3, is 
thrown upon the furnace 
grate, No. 6. Air enters 
as No. 4 to burn the 
coal, and the gases and 
smoke pass off as No. 9 
through the chimney. 
The utihzed heat, No. 11, 
reaches the boiler, No. 16. 
The feed water, No. 18, 
goes through the feed 
pump to the boiler and 
is there evaporated into 
steam by the heat. The 
steam passes through the 
steam pipe and past the 
control of the throttle- 
valve to the steam engine, 
No. 34, and does the 
useful work at its shaft, 




MECHANICAL ENGINEERING OF STEAM POWER PLANTS 








». " 



.5 so = 



u 



^=2, 



Ih 



V 



E — — 



60 "3 

.5 ■§ ~ * .3 S 

■ « 1^ 




15 



-^ 



p3:^=S^ 






2.E 






.§s 




INTRODUCTORY 




MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




INTRODUCTORY 9 

No. 37. The steam cooled down by doing work and reduced in pres- 
sure goes off through the exhaust pipe as No. 38. But from Fig. 2 
and Fig. 3 it is apparent that a power plant of any complete- 
ness can have many more elements or units than the few listed in the 
fundamental form, and that some of these will be introduced to 
secure economy of fuel and more perfect utilization of heat; others 
will tend to greater mechanical or plant efficiency; and others again 
will be for safety. Furthermore there will be a wide range for critical 
selection among the elements which are arbitrary or where alternative 
forms may be offered. Hence the field which this treatise will aim to 
cover may be divided as follows : 

I. Introductory and General. 

11. The Boiler and its Accessories. 

III. The Boiler Plant Auxiliaries. 

IV. The Steam Piping and its Accessories. 
V. The Engine and its Accessories. 

VI. The Engine Room Auxiharies. 

VII. The Operation and Testing of the Engine. 

VIII. General Considerations. 

IX. Historical and other Appendices. 



CHAPTER I, 

THE QUANTITATIVE BASIS OF THE STEAM POWER PLANT. 

5. Introductory. In every engineering problem involving the appli- 
cation of physical law, there are two distinct lines to be followed. The 
one is the functional study, concerned with the working of the machinery 
in practice : what it does and how. The other is the quantitative study, 
concerned with the necessary sizes of the organs or elements to do a 
given amount of work. 

The study in the following chapters is to be the functional research, 
in answer to the question, " How does each element work? " But to give 
definiteness and meaning to such study it will be worth while to glance 
briefly over the field from above and note some few quantities which 
enter into the problem of design, and which form, therefore, the quanti- 
tative basis of such a power plant. 

6. The Horsepower of a Piston Motor. The Cylinder Volume. The 
problem in industry always imposes a certain resistance to be overcome, 
and the effort of the motor must be powerful enough to exert the 
required force through the required space in the given time. If the unit 
of resistance is in pounds and the unit of space is in feet, the work from 
the motor will be the doing of a certain number of foot-pounds in a given 
time: or, if both members of the equation be divided by 33,000 (para- 
graf3), 

Work of motor in foot-pounds per minute 
33,000 ~ 

resistance in foot-pounds per minute 
^ 33,000 

or. Horsepower of motor = horsepower of resistance. 

The first term must be enough larger than the net resistance of the 
second term to overcome all friction and inertia and hurtful resistances. 
If the motor have the fundamental design of a piston traversing a 
cylinder it will be apparent that the pressure below the piston in 
pounds per square inch of area must be sufficient to lift the weight 
W in pounds: and to move this weight through the space m feet 
of its traverse at the speed specified (Fig. 4). If the pressure be 

10 



QUANTITATIVE BASIS OF THE STEAM POWER PLANT 



11 



P pounds per square inch, and the area be A square inches, the 
effort on the piston to hft the weight W is PA pounds. If the 
traverse in feet be L, then the work of one traverse is PAL, which 
balances the resistance work of the weight WL. If the traverse be 
made N times in one minute instead of only once, the total traverse 
is L N feet per minute, and the work of that minute is 

PAL N = Work in foot-pounds done in one minute, 

or the horsepower will be found by dividing both members by 33,000, so 
that 

jjp PLAN 
33,000 

If P were not the same in all traverses, or were not constant in any 
one traverse of the piston, no error would be made in using the mean 
value during the stroke or during the minute. In a 
crank-engine, the piston traverses L twice in one 
complete revolution, so that if a revolution counter is 
used instead of a stroke counter the quantity N must 
be twice the number of complete revolutions. 

The quantity L is in feet, and the quantity A is 
in square inches: if LA be divided by 144 the 
quotient is the volume of the cylinder swept 
through by the piston in cubic feet. But if the 
factor 144 is introduced into the denominator, the 
same factor must be introduced into the numerator 
to keep the equation true: hence the pressure per 
square inch, being multiplied by 144, becomes the pressure per square 
foot, or 



t. 




Fig. 4. 



H.P = 



Pressure in lbs. per sq. ft. X cyHnder volume in cubic ft. X N 



33,000 



P'V'N 
33,000 



For one stroke or traverse this becomes 

P'V 
H.P. 



33,000 



After the cylinder has been embodied in a metal casting 



33,000 

becomes a constant for that particular engine, which, if called K, gives 
the expression in either units, 

H.P. = PNK. 



12 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

The variables therefore with varying resistance can be only P and N. 
If the condition be imposed as is usual that the motor makes the same 
number of strokes each minute or turns at constant speed, then N 
cannot vary, and the only variable with varying resistance is the mean 
pressure P. 

The volume swept through by the piston, or the piston displacement, 
is the measure of the power of an engine, when the pressure P is given or 
fixed. The relations of stroke to diameter in standard designs of 
cylinders are fixed by convention between a stroke equal to the diameter 
and a stroke twice the diameter as limits, to secure the maximum 
volume or power with the minimum cooling surface of contact between 
hot steam and metal which can radiate heat away. 

7. The Work Unit and Heat Unit are Convertible. The Volume of 
Steam per Horsepower. The unit of heat is the quantity of heat required 
to raise one pound of water one degree Fahrenheit at the temperature of 
its maximum density near 39° F. This is called the British Thermal 
Unit. Some authorities prefer the value at 62° F. in raising the same 
weight to 63°. The researches of Joule and Rowland have shown that 
778 foot-pounds are the mechanical equivalent of one British thermal 
unit. In the metric units this is 428 kilogrammeters per degree Centi- 
grade. Hence if the equation for work in foot-pounds be divided by 
778 the quotient will be the equivalent heat units; or 

PLAN 
Heat units = 

778 

when the factors are known or assumed. But this assumes that the con- 
version of heat into work is perfect and is effected without loss ; which is 
far from the case in actual conditions. It gives the theoretical ideal 
for the heat which the coal should furnish to do the work in question. 
The relation between the actual coal burned in the plant, and the com- 
puted quantity by this calculation measures the efficiency of the plant: 

Computed coal consumption per horsepower ^^ ^ . 

or — -^ — ^ ^1- ^ — — = Heat efficiency. 

Actual coal consumption per horsepower 

If in the expression for the horsepower in the form 

H.P. = ^^ 
33,000 

the first term be made one horsepower and N be assumed and the 
pressure P per square foot is the mean during the piston movement, it 
would appear that 

33,000 

~P^~ ' 



QUANTITATIVE BASIS OF THE STEAM POWER PLANT 13 

or the volume of dry steam at the mean pressure P' which is required 
per horse power in this engine. But experience shows that the actual 
engine requires more than this by an amount which measures the losses 
from condensation and other causes in the cylinder and pipes and 
passages. It has been called the " missing water," and is the difference 
between the computed and the measured water per horsepower which 
the engine requires. When the computed volume has been corrected 
by this coefficient of condensation loss, then the weight of water per 
horsepower per hour can be ascertained from any reliable table of the 
properties of steam. (See Appendix, paragraf 566.)* The fine for the 
observed pressure being found, there will be columns for the weight of 
the cubic foot at that pressure; the weight of one cubic foot multiplied 
by the volume V in cubic feet per minute and this again by 60 minutes 
for the hour will give the pounds of water required by such a cylinder 
volume per hour. 

8. The Water Rate of a Steam Engine. The pounds of water to be 
furnished to an engine cylinder per horsepower per hour form a unit 
which is called the '' water rate " of this engine. Since this water is 
evaporated into steam by heat and this heat is obtained from coal which 
is paid for in dollars per ton, it is a means of reducing the operating 
cost of the plant or the cost of a horsepower to lower this rate. Many 
of the elements Hsted in the analysis of Fig. 2 are introduced for this 
purpose: such are the superheater. No. 26, the jackets. No. 42, the 
reheaters. No. 44, the condenser. No. 50, the types of complicated valve- 
gear and the use of the compound engine principle, as well as a number 
of the auxiHaries. This diminished water rate is secured by increased 
expenditure in first cost, a more complicated plant, and an expenditure 
of energy to operate it. But the net result is a gain where the coal 
consumption is large; or to put it otherwise, the gain is the algebraic 
sum of a loss made to effect the gain and the gain so secured. It 
becomes unsafe, therefore, to say what may be the water rate of an 
engine unless the factors are known which cause the rate to vary. In 
general terms, however, and over the broad range of practice, the- 
probable watet* rate of engines in good mechanical condition, with tight 
pistons and valves and well lubricated, would be not far from the values 
in the accompanying table. The size and capacity of the feed pump of 
Fig. 1 will be determined by the water rate of the engine. 

The reasons which lie back of some of these diminished water rates 
will be developed to some degree in the later chapters, or belong to an 

* Consult also Hutton, "Heat and Heat Engines," p. 206. Peabody, "Steam 
Tables." Kent, Mechanical Engineer's Pocket Book, p. 663. Suplee, Mechanical 
Engineer's Pocket Book. 



14 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

advanced study of the principles of the heat engine appropriate to the 
specialist and beyond the scope of this treatise. The record and 
reference here is to make it apparent why the simpler elements of 
the fundamental power plant enumerated in paragraf 4 became the 
complicated aggregate of Fig. 2. 

TABLE I. 

APPROXIMATE WATER RATES. 



Type of Engine. 



Triple-expansion, low-speed, condensing. . 

Triple-expansion, high-speed, condensing. 

Compound, low-speed, condensing 

Compound, high-speed, condensing 

Compound, high-speed, non-condensing . . . 

Large size simple, low-speed, condensing . 

Large size simple, low-speed, non-condens- 
ing ........ • 

Medium size simple, high-speed, condensing 

Medium size simple, high-speed, non-con- 
densing 

Small, simple, condensing 

Small, simple, non-condensing 

Pumps without fly-wheel, non-condensing 

Rotary steam engines, non-condensing 

Small steam turbines, condensing 

Large steam turbines, condensing 



Water Rate in Pounds per Horsepower 




per Hour. 


Probable Limits. 


Mean Assumable. 


18 to 


12 


16 


23 to 


14 


17 


20 to 


12 


18 


24 to 


16 


20 


30 to 


22 


26 


24 to 


18 


20 


32 to 


24 


29 


25 to 


19 


22 


35 to 


26 


33 


40 to 


30 


35 


60 to 


50 


'55 


140 to 100 


125 


100 




100 


60 to 


40 


50 


20 to 


12 


15 



Note. It may easily happen that variations in boiler pressure, expansion, valve 
gear and speed will produce greater variations in water rate in any particular case 
than the variation in type as listed on the lines of classification above. The use 
of the average figure is therefore dangerous in inexperienced hands. 



9. The Heating Surface of a Steam Boiler. Transfer of Heat. The 

heat liberated in the chemical union of oxygen with the carbon and 
hydrogen of the fuel in the boiler furnace is expended in heating up the 
fuel itself and the air which supports the combustion, and the hot 
gases which result from the process. This heat must be absorbed 
by a transfer to the metallic plates of the boiler shell and to the water 
and steam. Heat is transferred from a hotter to a cooler body by 
radiation from the solid matter of the fire and the glowing solid matter 
in the flame; it is transferred by contact from the invisible hot gases 
which have no radiating effect. There will be some transfer to the masses 
of brick in a brick-setting, and some transfer to the external air from the 



QUANTITATIVE BASIS OF THE STEAM POWER PLANT 15 

boiler itself by radiation and contact (Fig. 2, No. 8); there will be 
some heat potential carried off in the fines and chimney unused because 
unabsorbed (Fig. 2, No. 15), and some energy will be used to carry the 
burnt gases away (Fig. 2, Nos. 9 and 49). There are also losses 
Nos. 7, 13 and 14, which are hardly recoverable. But the adequacy 
of the absorbing metal surface of the boiler or heater (Nos. 10 and 11) 
must be depended on to reduce No. 15. (See paragraf 144.) 

Transfer of heat is effective in proportion to the difference of 
temperature between the hot and the cooler body; hence the heating 
surface of the boiler which is the cooling surface as respects the fire, 
flame and gas should have water on one side of it while exposed to the 
heat on the other. Heating surface is therefore the area of metallic 
plate of the boiler shell which has water in contact with it on the one 
side and is exposed to radiation from fire and flame and to contact 
with hot gases upon the other. If a part of the heating surface becomes 
uncovered by lack of water, it becomes as nearly red-hot as possible, and 
is not only ineffective (since the specific heat of steam is less than half 
that of water), but by its softening by the heat and its oxidation and 
the sudden contraction when it cools, it becomes a source of danger. 

The number of square feet of heating surface to supply a required 
weight of water evaporated into dry steam to supply a cyUnder of a 
given capacity is a matter of test and experience. The accepted figure 
is to give one square foot of heating surface for each three pounds of 
water to be evaporated per hour, which would result in llj to 12 square 
feet of such heating surface to each 30-36 pounds of water to be evapo- 
rated per hour, which is the usual allowance. 

10. The Horsepower of a Boiler. A. S. M. E. Standard. The term 
horsepower is not properly applicable to a steam boiler, except in the 
sense of a capacity to supply to an engine the weight of steam per hour 
to enable it to develop a rated horsepower. Table I shows, however, 
the wide range of capacity demanded as the type of engine and the 
scope of the auxiliaries in the plant vary. The best that can be done 
is to reach a convention as to the figure for water rate to be used in 
computations so that all may refer to the same unit. Such a unit 
was agreed to in 1886 in a Committee of the American Society of 
Mechanical Engineers and is therefore known as the A. S. M. E. Standard. 
The water rate of such a conventional engine was fixed at 30 pounds 
of water when the evaporation took place at 70 pounds pressure and 
with a preheated feed-water (Fig. 2, Nos. 17 or 46) at 100° F. This 
is equivalent to an evaporation of 34.488 pounds of water at 212° or 
at atmospheric pressure with the feed-water at 212° F. 

The square feet of the heating surface will be usually related to the 



16 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

square feet of the grate surface in certain definite relations (para- 
graf 12). 

11. The Pounds of Coal to Evaporate a Weight of Water. Every 
pound of fuel has a capacity to liberate and transfer on its complete 
combustion a certain number of units of heat. The value of this 
capacity is called its calorific power. It is measured experimentally 
by an apparatus called a fuel calorimeter. 

From steam tables (paragrafs 7 and 566) it appears that to make 
water into steam it must first be raised as water to the boiling point 
at that pressure and then changed into steam at that pressure; the 
units of heat for each pound at each pressure are known. At atmos- 
pheric pressure, for example, 965.7 units are required to make one 
pound of water at 212° into steam at 212°; if the feed water is colder 
than 212° so many additional heat units per pound will be required. 

If the transfer of heat could be complete, and the calorific power 
of the fuel had been ascertained, the pounds of water per pound of 
coal would be 

Calorific power of fuel in heat units 



Pounds of water from and at 212° = 



965.7 



For a fuel of 12,000 heat units (a usual value) the water evaporation 
would be 12.4; for the best American coals with little ash, such as those 
from Georges Creek, Md., or the Pocahontas veins in W. Va., the calorific 
power of 14,000 gives a theoretical evaporation of 15 or 14 pounds. 
In the actual furnace, however, neither transformation nor transfer are 
perfect; hence from 9 to 7 pounds of water per pound of coal are good 
results. See Tables II and III below. This means '¥ = 3.3, or V = 
4.3 pounds of coal per boiler horsepower per hour or per engine horse- 
power if its water rate is 30. If its water rate is 12 or 16 the coal per 
horsepower per hour becomes V = 1.3 or V^ = 2.3. If the evapora- 
tion rate falls, the coal rate rises, of course, to furnish a given weight 
of steam. When the unit becomes 1000 horsepower and the coal con- 
sumption becomes 2300 pounds, or over one ton per hour, both the 
water and the coal rate become financially significant, and it pays to 
invest money in auxiliaries to save coal, water, and labor. 

12. Grate Surface to Burn a Weight of Fuel in a Given Time. Rate 
of Combustion. Since the weight of coal to evaporate the required 
weight of water is known, it follows that if the water is to be evaporated 
in a given time — an hour — the required coal must be completely 
burned in that same time. There must be a grate area of sufficient 
extent to accommodate the weight of fuel needed in an hour, but the 
rate of combustion must be so related to that area that the full amount 



QUANTITATIVE BASIS OF THE STEAM POWER PLANT 



17 



of heat shall be liberated from that weight. This rate of combustion 
is usually given as the number of pounds of coal burned per square 
foot of grate per hour. It is rarely or never less than 10-12 for 
anthracite coal and 15-18 for bituminous, and this is for chimney 
draft.. With forced draft from pressure blowers it may rise to 60 or 
even to 125 pounds. When so much more heat is liberated per unit 
of time, the fire is intensely hot, and it becomes more difficult to 
absorb the heat; the evaporation rate is usually less with a high com- 
bustion rate. The heating surface ratio increases greatly with high 
combustion rate. The following tables give some relations: 



TABLE II. 

RATIO OF HEATING SURFACE TO GRATE SURFACE. 



Kind of Boiler. 


Grate Surface. 


Heating Sur- 
face. 


Combustion. 

Rate in 
Pounds per 
Square Foot 

Grate. 


Internally fired stationary 


1 


26 to 33 
40 to 50 
40 to 50 
50 to 60 
30 to 70 
60 to 70 
35 to 65 


10 to 20 


Internally fired stationary 


20 to 40 


Marine boilers, internally fired 


15 to 30 


Marine boilers, internally fired 

Portable boilers, internally fired 

Locomotive boilers, internally fired 

Water tube boilers, externally fired 


20 to 50 


40 to 100 
15 to 25 



TABLE III. 

RELATIVE EVAPORATION BY SOME AMERICAN COALS. 



Source. 



Kind. 



W. Va. Pocahontas Semi-bitum's 

Youghiogheny, Pa ... Bituminous. . 

Hocking Valley, O do 

Big Muddy, 111 do 

Mt. Olive 111 .do 

Lackawanna, Pa . . Broken an- 
thracite. 
.... Do No 1 buck- 
wheat. 
... Do Ricp, anthra- 



cite. 



Calorific 
Power. 



14,600 
13,500 
11,700 
11,700 
9,900 

12,700 

10,700 

9,200 



Pounds of 
Coal per 

Square 
Foot 

Grate. 



15 
17 
18 
20 
20 

15 

13 

12 



Heating 
Surface to 

Grate 
Surface. 



45 
48 
45 
50 
45 

35 

32 

30 



Pounds of 

Water per 

Pound of 

Coal at 

212°. 



9.5 
8.7 
7.6 
7.6 
6.4 

8.5 

7.5 

7.0 



18 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

13. The Cost of a Horsepower. There will be two costs to be con- 
sidered under this term; the one is the cost of the plant per horsepower 
to install, and the other is the cost per horsepower to operate when 
installation is complete. Obviously figures of cost must be subject to 
wide variations according to the standard before the mind of the com- 
puter. A cheap engine of small or medium power costs about $14 per 
horsepower; a more expensive engine with better valve gear and more 
economical performance costs about $25 per horsepower. The boiler 
unset to supply the cheap engine will cost about $9 per horsepower 
capacity; a larger boiler in its setting costs from $14 to $15. Exclusive 
of the buildings to house them there is a range between $23 and $40 per 
horsepower. With buildings included the range is from $45 to $75 per 
horsepower for installation. 

The charge or buying and selling value for a horsepower per annum is 
open to the same wide limits. A full and complete computation on the 
basis of mill conditions in New England gave a production cost without 
profit added, varying from $24 to $33. A low cost when profit is 
charged is $35 per annum. When a large investment interest must be 
provided for, the price rises where coal and labor are costly to $75 per 
annum per horsepower. In many of the cities the large electric pro- 
ducers sell current at 2 to 2 i^ cents per kilowatt hour. If there are 10 
working hours of the day for 300 days, or 3000 working hours, the 3000 
kilowatt hours will cost $75 per annum, or at the rate of $56 per horse- 
power. Private plants claim to be making their own current at $0.85 
per kilowatt hour, charging themselves no profit for dividends: this 
makes the yearly cost per horsepower as low as $42. These figures must 
be subject to frequent revision as conditions change. 

14. Summary and Conclusions. It has been the purpose in the 
foregoing synthetic and quantitative study to give a glance over the 
entire field to the ultimate purpose of the plant before turning to the 
analytical study of details. The object of the plant is to make money or 
to be a successful investment. There are certain elements or units 
which are inevitable, or without which there would be no plant (para- 
graf 4 and Fig. 1); the analysis shows an apparent complication or 
multiplicity of detail (Fig. 2), in the study of which the reader and 
student might lose sight of the fundamental unity, unless this inclusive 
outlook had been first given him. From this point on the study is 
analytical, of each unit by itself. The student is expected to put 
the element in its place in the general scheme as being of necessity or 
merely desirable according to the key which these chapters should have 
put in his hands. 



PART 11. 



CHAPTER II. 

THE BOILER. FORMS, MATERIAL AND MANUFACTURE. 

20. Introductory. The fuel introduced and burned under the boiler 
is the source of energy in a steam plant and therefore the furnace and its 
attachments should logically be the first objects of study. The capacity 
of the furnace to burn fuel and the capacity of the fireman or stoker 
to introduce it are the limits set, beyond which the plant cannot furnish 
power under those conditions however big the boiler itself may be. 
On the other hand the boiler is typically so much more massive than the 
furnace details and the latter are structurally adjusted to the boiler for 
this reason, that these causes make it convenient to take up the boiler 
first and its grates and furnace afterward. The boiler will be the same 
furthermore whatever the fuel, whether coal or gas or liquid hydro- 
carbon is used, while the grate or furnace will be varied. 

21. The Function of the Boiler or Steam Generator. The steam boiler 
or pressure generator in a power plant has three functions. First, it 
must receive, store and control the medium which is to be used to trans- 
form the heat energy of the fuel into pressure or into mechanical energy 
by its expansion, k econd, it is to receive and absorb the heat energy 
of the fire with the greatest completeness and economy or with the least 
unproductive waste of heat. Third, it must serve as an accumulator or 
equaUzer between the slowly varying or continuous heat supply from 
the fire and the rapidly varying or intermittent demand of the engine or 
consumer of steam. In the steam boiler plant, the medium is water; 
but in the general case of an external-combustion engine (paragraf 2), 
it may be any convenient cheap innoxious vapor which expands readily 
by heat so as to produce pressure. The vessel must be closed to retain 
the pressure when generated and must be tight against inconvenient 
leakage and loss. It must not be unduly attacked by corrosion from 
the medium. 

The generator must not be injured by the heat of the fire, and expan- 
sions and contractions due to variations of heat in the water or the fire. 

19 



20 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

The surfaces exposed to heat should be metalHcally clean or free from 
coating or incrustation outside or scale of precipitate from the water 
inside. The shape should be such as to receive and absorb and transmit 
exterior heat to the water within very rapidly, since the coal and flame 
do not last long, and the hot gases should be moving quickly through 
fire and furnace to make room for fresh oxygen as needed. The metal 
surfaces surrounding the water should be as thin as consistent with 
safety, because the thicker the plate the greater the chance for the outer 
layer to get further from the lower temperature of the inner layer, which 
is close to the water. What is desired is that the outer layer shall be as 
nearly as possible at the temperature of the cooler water which it 
encloses. Then the transfer of heat from hot gas or radiating fire 
and flame is most efficient, and the gas is most effectively cooled 
before it escapes the boiler setting and passes into the chimney. 
This principle lies at the base of the efficiency of small diameter 
boiler units. 

Radiant heat from the solids of the fire and from the volume filled by 
a luminous flame is the most effective to heat the water, not alone as 
a matter of laboratory observation with luminous points, but because 
the transfer is not affected by interferences, and every cubic inch of 
radiating mass acts as if the other cubic inches did not exist. In 
transfer by contact from non-luminous gases on the other hand only 
those layers of gas which come in thin films into contact with the metal 
to be cooled by it do any work. Any cubic inches of hot gas which 
do not touch colder metal go out unreduced in temperature and 
ineffective for heating, since hot gas does not radiate its heat at all. 
This is why the flaming or semi-bituminous coals are the best steam 
makers (paragraf 12). This explains why retarders in boiler tubes are 
of any advantage (paragraf 58) ; it explains the effectiveness of nests 
of water-tubes (paragraf 80), and the necessity and economy of small 
fire-tubes where the draft is powerful and the velocity of the gases is 
high (paragraf s 56, 70) 

33. The Storage of Energy in a Steam Boiler. The type and form of 
the steam boiler are more determined by the opinions of its designer 
respecting the third function of the boiler than by any one of its duties. 
The demand for steam for the engine cylinder is confessedly irregular, 
varying from the maximum capacity of the furnace to supply energy 
down to zero at intervals and fluctuating all the time on either side of a 
mean demand. The supply of heat from combustion of solid fuel is not 
an instantaneous process, although with gas and oil fuel it is very 
nearly so. But the transfer of heat to water and its volatilization into ' 
steam gas is again a process never normally instantaneous. The volume 



THE BOILER 21 

of steam gas actually on storage in the boiler at any time is not large 
as compared to the cylinder volume which draws from it, and a few 
strokes of the engine would so exhaust it if it were a permanent gas only, 
that the pressure would fluctuate inconveniently and fall below an 
admissible limit. But it must be remembered that the heat energy 
from the fuel is stored in the heated water and not in the steam gas. 
This is by reason of its high specific heat — it takes more units of heat to 
heat a pound of water than any known convenient and cheap natural 
substance — and by reason of the physical relation of the boiling point 
of water to its pressure. 

For the steps which succeed each other in steam making are as 
follows. First, when the cool water is pumped into a vessel partly full 
of water and with a fire under it, the water is gradually warmed and 
expands in the process as water until the boiling point due to that 
pressure is reached. This boiling point is of record for every pressure 
in steam tables (paragraf 566), increasing as the pressure increases. 
Second, a pause in which no further expansion or increase of sensible 
temperature occurs, during which the additional heat necessary to 
change water at that pressure and temperature into steam at that 
pressure and temperature is absorbed by each pound of water. Third, 
when this necessary heat has been taken in, the water changes into 
steam gas in bubbles, through the mass and at the level surface. This 
is boiling or ebullition and is most active where the water is hottest by 
reason of most effective transfer of heat, or where the pressure is lowest, 
if there are any reasons why it is not uniform throughout. Such steam 
gas frees itself from the water by reason of the much greater weight of a 
volume of water than an equal volume of gas, and the layers of gas get 
on top of the water, pressing it down. If the boiler is closed, this 
volume of steam gas, being larger than the space it formerly occupied as 
an equal weight of water, produces an increase of pressure in the water- 
surface, causing, fourthly, a cessation of the bubbling or manufacture of 
gas until additional heat is supplied from the fire to meet the increased 
boiling point due to the increased pressure. Hence, fifthly, the pressure 
and temperature continually increase by stages until some gas is drawn 
off to the engine or through a relief or safety valve or the capacity of 
the fire to supply further heat energy is surpassed. When the boiler is 
not completely closed, but the throttle valve to the engine is con- 
tinuously open, there is no pause for steps two and four, but the process 
is continuous if the fire is adequate. If the fire is too fierce, or too much 
energy per unit of time is entering the water, the pressure rises in spite 
of the demand; if the fire is weaker in supply of energy than the demand 
for it from the engine, the pressure falls. 



22 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

The existence of the second step, which the fourth only repeats, 
explains why the mass of water is the storage element in the boiler. 
If the mass of water is large and has stored in it a great number of heat 
units, the water will keep on forming steam (albeit at continually but 
slowly reduced pressure), after the fire has been withdrawn. It will 
bridge over the time required to slice the fire and remove clinkers and 
put on fresh fuel. It enables the fire to be kept by the process of bank- 
ing over night, so that a mass of highly heated water is ready for early 
demands, and yet the pressure may not have risen inconveniently in 
the interval. Where the wide fluctuation of the steam pressure is 
regarded as objectionable, and where the fuel supply at the same time 
is irregular or intermittent, large water volume must be provided. 
Such large masses of water, on the other hand, make slow steam-makers 
of such boilers, and when by rupture of the containing shell the stored 
energy is all released at once, there is so much force to be expended in a 
very short time that the most appalling destruction is likely to occur by 
the throwing about of large masses of metal and the disengagement of 
great volumes of the steam gas from such water. 

In a middle class will be those boilers in which a smaller mass or 
weight of water is enclosed under pressure, and the surface exposed to 
heat and to transfer such heat is relatively large. Such are boilers in 
which the water space is full of tubes carrying hot gases, and dividing 
the water into smaller volumes by their displacement. Such boilers are 
rapid steam-makers, or quick-steamers. Pressure accumulates rapidly, 
and disappears rapidly on demand for steam. They reach a dangerous 
pressure quickly when not watched, with its attendant danger of rupture 
if it is not relieved. But the pressure falls quickly when relieved and 
when they rupture there is not so much water to make so much steam 
gas and the disaster and destruction are not so great. 

In a third class are what are called flash or semiflash boilers, in which 
there is practically no water on storage, or very little. The heating 
surface — usually in coils of steel pipe — is so great that the interval 
required for the passage through the steps or stages of evaporation is 
inappreciable or too small to be measured, and water pumped into the 
generator appears to flash into steam-gas. Such boilers have no steady 
steam pressure at all, but are subject to pulsations of pressure which 
synchronize with the strokes of the feed pump. There can be no 
explosion from accumulated energy for there is none in a true flash boiler. 
As the excessive fluctuations are inconvenient, the semiflash type is 
more in use, in which there is some water present in storage, but less 
than in the preceding type. As soon as all water has become steam the 
absorption of heat becomes much slower, and the inconvenience then is 



THE BOILER 



23 



mainly from the injury to the heating surface from the overheating to 
which it is subjected. 

It is plain that to meet the storage function of the boiler, the prime 
requisite is sufficient strength to resist internal pressure, tending to pro- 
duce-rupture or excessive deformation. The problems of theory will, 
therefore, be those of physics as respects transfer of heat, and those of 
mechanics respecting stresses and resistance in the shapes and materials. 

23. The Problems of Physics Respecting Transfer of Heat. The 
conditions to be filled for effective transfer are: 

1. The difference between the temperatures of the absorbent body 
and that parting with its heat must be a maximum at all the stages of 
the process. That is, the water when it is as warm as it is going to be 
should then be nearest to the hottest fire or gases. If the hottest water 
meet only the coolest gases, the transfer as a whole process is less effec- 
tive. ' This means generally that the currents of gas and of water should 




Fig. 5. 



flow in opposite directions on the opposite sides of the plate, the coolest 
water coming in at the end furthest from the fire. This also makes it 
desirable that the water should '' circulate " within the shell, the 
heavier, cooler water tending to go to the lowest part and displace 
upward the warmer water and that which by reason of steam gas 
bubbles in it is hghter than the soHd water. Fig. 5 illustrates how 
these currents will flow in a large mass of water with steam above the 
water and fire below at the left hand. 

3. The surface of metal between the hot element and the water 
which is to absorb the heat must be in the best condition to transfer 
this heat. That is, it must be as thin as is safe and convenient, and 
it must be metallically clean or free from any non-conductors of 
heat, especially those which would keep the water from effectively 



24 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



*isi 



Fig. 6. 



^ 



touching the plate. The outside surface next the fire is Uable to a 
coating of tar, or soot, or flue dust, or a mixture of all three. The inside 
is liable to a coating of mineral scale deposited from the water as it is 
boiled; to a film of oil or grease if these are not effec- 
tively separated from the feed water; and to a film of 
steam gas which fails to be carried up to the surface 
by the convection or circulation. Anything which 
keeps the water from the steel will permit the latter 
to overheat to its detriment, and impedes the 
transfer. Vertical surfaces or those inclined at small 
angles from the vertical, are least subject to such 
deposits, and vertical circulation is most direct and 
active. On the other hand, small vertical tubes of 
any length closed at the bottom are liable to a slug- 
gish or indeterminate circulation. If a large steam 
bubble forms, it may be unable to get out except by 
forcing out all the water above it in the tube. By 
inclining the tube, the steam rises to the upper seg- 
ment and follows this to the top ; a descending current 
of water follows the lower elements of the tube. The 
circulation must carry away or wash off the steam gas 
from the heating surface, because the specific heat of 
the steam is less than that of the water, and the 
heating surface is less effectively kept down in tem- 
perature. The Field tube (Fig. 6) used in fire-engine 
and tug-boat boiler practice in America and in English and conti- 
nental practice secures a determinate circulation by having solid 
cooler water descend through the inner tube while the bubbles rise 
against the walls of the hotter exterior tube. If circulation stops at 
any time, soUd matter may gather at the bottom; and if it forms 
hard enough not to be washed out, the tube burns at the end. 

3. The disengagement of steam gas from the upper water surface 
must be free. If the area is small, the effort of the steam to free itself 
from the water is impeded when the boiler is driven. Hence unnec- 
essary effort is required, and the bubble leaves the water explosively 
and entrains spattered water mechanically with it. This is called 
foaming or priming and not only is the steam wet and therefore 
wastefully used, but the water may cause breakage of cylinder cast- 
ings, or bed-plate, or bend or shear or break forgings in the mechanism 
(paragraf 377). 

4. The surfaces receiving radiated heat should be normal to such 
radiating volumes to receive the full effect of transfer by this method. 



THE BOILER 



25 





Water-Tube 



When the fire is horizontal or the current of flaming gas, the surface 
over such fire or flame is the most effective. Hence the metal should 
be concave downward for best effect. But this shape is ill-adapted to 
resist pressure from within, and has not been used for external shells 
since the days of very low pressures (Fig. 7). In horizontal tubes or 
flues the upper part meets this requirement, and the lower part is apt 
to be ineffective by ash deposit. When the water is inside and the fire 
and flame are outside and below it, the principal transfer is by contact 
in any event (Fig. 8). 

5. The gas must remain long enough in contact with the metal for 
the process of progressive transfer to take place. Strong draft requires 
more heating surface than with gentle draft, since not only 
will the gases be hotter by reason of the higher combus- 
tion rate, but the velocity may compel them to reach the 
chimney before all possible transfer has 
been made. 

6. The gases in contact must be 
divided into thin films and so touch 
the plate, giving every cubic inch of 
such flowing gas a chance to give up 
the heat it carries. This is very effec- 
■p^^ 7^ tively done with small tubes in fire- 

tube practice, and in water-tubular 
designs by having the axes of the tubes at right angles to the flow 
of the gas, so that the tubes act as baffles, and subdivide the currents. 
7. The flaming currents of gas must not be so lowered in temperature 
by contact with cooler metal as to arrest the chemical processes of 
combustion in such flames. If the transfer under these conditions 
is so effective that the gases are cooled below the temperature of 
ignition or of combination with oxygen, the flame becomes a smoke, 
combustible goes off unused, and the effect of the flame is lost. This 
will be referred to again under smoke prevention (paragraf 129). 

Of course the furnace is assumed to meet the requirements of com- 
plete combustion from the chemical point of view, supplying so much 
atmospheric air as w^ill furnish the weight of oxygen required to form 
CO2 gas and Kfi from the weights of carbon and hydrogen supplied 
per minute or per hour. This opens up the well-known computations 
of chemistry, when the atomic weights of carbon, hydrogen and oxygen 
are given, to discuss which completely would be aside from the present 
purpose.* 




* See The Gas Engine, pp. 22, 23, for greater extension of treatment. 



26 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

24. Combustion. The typical computations for combustion include: carbon, C, 
burning to carbonic dioxide, CO2; atomic weight of C = 12; atomic weight of oxy- 
gen 16 

+ 0^= CO2; 12 + 32 = 44. 

Hence the oxygen is ff of the weight of carbon supplied ; if the weight of carbon is 
one pound, the weight of oxygen is 2.66 pounds. If there is too little oxygen 
supplied, the carbon may burn to carbon monoxide, CO; then C + O = CO, or 
12 + 16 = 28, and the oxygen weight in pounds is ^| of the pound weight of carbon. 

If hydrogen (H, atomic weight = 1) burns to HoO or steam vapor H2 + 0=H20; 
2 + 16 = 18; or one pound of hydrogen demands ^ = 8 pounds of oxygen. 

With compounds made up of cartjon and hydrogen, the process is identical. 
Assume the gas ethylene, C2H4 ; then 

C2 + O4 = 2 CO2, or 24 + 64 = 88 

H4 + Oo = 2 H2O, or 4 + 32 = 36 

Totals, 28 + 96 - 124. 

The gas weighing 28 requires |f of its weight of oxygen, or one pound requires 3.43 
pounds of oxygen. 

To furnish air for these weights of oxygen, one pound of air at the temperature of 
melting ice has 0.236 pounds of oxygen in it. Hence V%V = 4.25 times as much 
air must be furnished as there is oxygen required. Hence for carbon 2.66X4.25 
= 11.3 pounds of air are required; and for hydrogen 8 X 4.25 = 34 pounds of air. 
For the compound, 3.43 X 4.25 = 14.58 pounds of air. 

If one pound of air occupies 12.39 cubic feet at this temperature: 

C requires 11.3 X 12.39 = 140 cubic feet of air. 

H requires 34 X 12.39 = 421 cubic feet of air. 

C2H4 requires 14.6 X 12.39 = 180 cubic feet of air. 

35. The Problems of Mechanics Respecting Form and Internal Stress. 

The simplest function of the boiler as a storage reservoir for pressure is 
that of resisting such internal fluid pressure: — that of the water with 
the vapor tension upon its surface acting downward, and that of the 
vapor tension acting upward and laterally. Such tension in any high 
pressure boiler is practically equal in all directions, as the weight of the 
water per square inch becomes inappreciable in comparison with the 
other force. Such internal pressure tends first to produce deformation 
if the containing envelope is capable of changing shape under equal 
pressure in every direction until a permanent shape is reached. After 
that without change of form the equihbrium of effort of the pressure and 
of resistance in the material forming the envelope will be reached at a 
point called the bursting pressure, beyond which the resistance of the 
material is overcome and the shell ruptures at some point where it 
happens to be accidentally weakest. The question is therefore two- 
fold: what is the permanent form of a closed vessel under internal 
pressure; what fixes the rupturing pressure of such permanent form? 
The permanent form for such a containing envelope of pressure is 



THE BOILER 



27 



the sphere. The internal pressure at every elemental area of the inside 
surface is decomposed equally and symmetrically in every direction, 
in the plane of the tangents to such surface at that point. The resist- 
ance of the shell from its tensile strength is in the line of these tangents. 
The elastic deformations of the material under these stresses cause the 
sphere to grow larger in diameter in every direction equally, but do 
not change the shape. The same conditions continue till the sphere 
ruptures. How will it rupture? If at some point on the great circle 
of the sphere a weak spot occurs, a spht or crack develops where the 
continuity of the metal is broken. Instantly the strain at the two ends 
of such crack or split becomes greater than it was just before, supposedly 
then near or at the limit of such resistance, because the fractured area 
is holding no longer and the pressure has 
a moment or lever arm to prolong the 
spht around the circle. The sphere then 
parts into two hemispheres, unless the 
pressure is so released at the break that 
there is not force enough to complete the 
tear in a ductile and homogeneous shell. 
If Fig. 9 represent a section of such a sphere 
in the plane of the page, the part above 
the horizontal AB tends to leave the part 
below it under stress, the direction of the 
line AB relative to the horizon being determined by the location of 
the weakest point at one of its ends. 

The sphere was early used as a form for the boiler, not only because 
the boiler is the derivative of the domestic kettle and the spherical con- 
cept was thus famihar to the first designers, but because the early 
boilers of soft copper sheets took this shape of themselves. It is not 
well-adapted to receive the heat of fire and gases, nor to keep the hot 
gases in prolonged contact with it (paragrafs 23-5) ; the only modern 
use has been in sectional forms where comparatively small cast-iron 
spheres were jointed together into banks or aggregates of such units, 
the ultimate shape of such aggregates becoming a parallelopidon and 
not the sphere. But the same permanence of shape under internal 
pressure attaches also to the cyhnder. If the enclosing heads be made 
hemi-spherical, the same results are retained as with the sphere, except 
that quantitatively the stresses are modified. Such cylindrical boiler 
utihzes the heat of the gases much more adequately, and is easier to 
support and to set. Fig. 10 shows the type of such boiler of per- 
manent shape, known historically as the " egg-ended " boiler, as its 
heads were spheroids. The flat head is much easier to make in 




Fig. 9. 



28 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

heavier material, and hence the advantages of this shape are rarely 
utilized. 

The sphere and the cylinder offer the same advantages of resisting 
uniform pressure without deformation when the pressure is from without 
radially inward, tending to collapse the cyhnder or sphere. Here, 
however, it is imperative that all deformation be prevented, since the 
moment such a strained envelope loses the true circular section the 
areas exposed to pressure are no longer equal in every direction. The 
flattened areas have more aggregate pressure on them than the curved 
areas, and the flattening is progressive until the opposite sides come 
together or the metal tears. This trouble must be faced in large internal 







Fig. 10. 

flues used as furnaces in types hereafter to be discussed and great pains 
must be taken to keep such cylinders as arches up to their proper shapes 
by stays or stiffening rings around them (paragraf 61 ) . 

Flat surfaces exposed to fluid pressure bend or deflect if fastened at 
the edges only, bulging outward until the stress in the plate due to its 
flexure resisted at the edges exceeds its tensile resistance. Such defor- 
mation must be resisted by reinforcing the low resistance of these 
plates to such flexure, either by stiffening bars or beams or by '' stays," 
which are rods attached to the flexible surface at one end and fastened 
at the other to some point which is rigid or which tends to move under 
pressure in opposite sense. The tension in the stay replaces the lacking 
capacity of the flat surface. (See Stays, under paragraf 44.) 

26. Values of the Stresses in Boiler Shells. Thickness of Boiler Plate. 
Assuming the cylindrical form for the boiler with flat ends it will be 
exposed to pressure, or its inside tends to part along a roundabout or 
ring seam by pressure against the heads, and it tends to part along a 
longitudinal seam and open out into a flat plate. If the pressure on 
each square inch be denoted by P, and the diameter of the cylinder be 
D in inches, the area exposed to pressure to blow out the head or rupture 
a ring seam will be the area of the head in square inches multiplied by 
the pressure on each square inch: 

PA = Pizr'' == Pti ~ ' 
4 



THE BOILER 29 

The resistance to this pressure is offered by a ring of the boiler-metal 
whose area is 

2 Ttrt 

when t is the thickness. If /be the tensile strength per square inch, the 
rupturing force just balances the holding resistance of the material 
when 

Ptz — - 2 nrtf. 
4 -^ 



This simplifies into 



PD = 4 tf. 



For the resistance to rupture along a longitudinal seam it can be proved 
mathematically that the tendency to rupture in any plane will be the 
sum of the components of the normal pressure at every point which are 
perpendicular to that plane.* Therefore on each inch in length of such- 
longitudinal seam the total pressure is PD. This can also be made 
clear by the expedient of imagining each semi-cylinder of the boiler to 
be nearly filled with a solid material like wood, and that the pressure 
P is introduced into the narrow space left between the two semi- 
cylinders which are held together by the enveloping ring of boiler-plate 
(Fig. 9). The resistance to separation of these semi-cyHnders is the 
sum of the areas of boiler-plate at the two sides, multiphed by the 
tensile strength per square inch of that plate. This resistance is de- 
noted by 2 tf when the ring has a length of one inch. Hence the 
equiUbrium of bursting pressure and resistance along a longitudinal 
seam is reached when 

PD = 2 tf. 

It will be noticed that the boiler is twice as strong against blowing out 
the head or rupturing a ring seam as it is against rupturing along the 
longitudinal elements of the cylinder. This explains why boilers are 
double-riveted or are made with special joints for their longitudinal 
seams. 

The above calculation is for sohd plate, or for welds which are as 
strong as the solid plate. Where riveted seams are used an allowance 
must be made for the reduction of the value for / due to the weakening 
caused by removing the metal at the rivet-holes, which the rivets do not 
replace. This factor is called the '' Efficiency." See paragraf 40. 

Boilers are usually designed with a factor of safety of six in their 

* See paragraf 36 at end of this chapter. 



30 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

shells; or in other words, the working pressure is one-sixth that at which 
the shell would be expected to rupture from internal pressure. 

Boiler-plate can be bought of all thicknesses, but it is usual when the 
calculation brings out an inconvenient figure to pass to that practical 
thickness which is next above. Usual thicknesses of plate are, in 
fractions of an inch: 

3 1 5 3 7 1 9 5371-1111 

It is inconvenient to handle, curve, and rivet plate thicker than one and 
one-half inches. The difficulty of manufacturing thicker plates also 
stands in the way of their use. A less thickness can be made to serve 
by using a smaller diameter. An allowance of -^ of an inch is generally 
made above the computed theoretical thickness for the effect of corro- 
sion, external and internal, while still leaving the boiler of full strength 
until that w^astage has occurred. 

37. Materials for the Boiler Shell. Specifications and Tests. The 
material of which the shell is made must not only withstand the 
internal pressure stresses, but also those due to expansion and con- 
traction by changes of temperature within wide limits. The stresses are 
often sudden, are unequal in different parts of the shell and therefore 
local in their action, and their magnitude may reach the limit of the 
resisting power of the shell if little or no time is given to yield to them 
by changes of figure of the plate. Such sudden changes come from cold 
feed-water suddenly pumped into a partially empty and, perhaps, over- 
heated shell, and from an inrush of cold air into a fire-box from a 
suddenly opened fire-door in cold weather. Hence the boiler material 
must not only have tensile strength, reasonable conductivity and ease of 
manufacture, but it must be ductile (the term used in the sense of 
being not brittle), so as to stretch and yield without danger of sudden 
breaking. 

The only materials in universal acceptance are three grades of soft or 
low carbon steel, made by the open-hearth process, acid or basic, and 
meeting specifications as in table on page 31 for the qualities known 
as Flange or Boiler Steel, Fire-box Steel, and Extra Soft or Rivet 
Steel. 

It is generally considered undesirable for the engineer to limit the 
manufacturer respecting his processes or chemical methods of attain- 
ing the result, and to hold him for the result only. Hence while the 
carbon-steels referred to above will be usually lower in carbon than 
0.50, it is quite hkely that alloy steels containing nickel and other 
strengthening elements will come into use with lowered prices, pro- 
vided such strong steels are not brittle under stress and heat. Other 



THE BOILER 



31 



materials for boiler steels have been of significance in earlier uses, 
such as copper, cast and malleable iron and wrought iron (see para- 
graf 37) and offered some advantages at that time. 



TABLE IV. 

SPECIFICATIONS FOR BOILER STEELS. 



Element Specified. 



Tensile strength pounds square 
inch 

Yield point not less than 

Elongation per cent in 8 inches 
not less than 

Phosphorus not to exceed 

Sulphur shall not exceed 

Manganese 



Flange Steel. 



55,000 to 65,000 
i Tens. St. 

25 

Acid 0.06 

Basic 0.04 

0.05 

0.30 to 0.60 



Fire-box Steel. 


52,000-62.000 


i Tens. St 




26 




AcidO. 


04 


Basic 


03 





04 


0.30 to 0. 


50 



Extra Soft Rivet 
Steel. 



45,000-55,000 
i Tens. St. 



28 
0.04 

0.04 
0.30 to 0.50 



The material shall be tested by testing machine, and by bending and for homo- 
geneity- The bending test shall be made both cold and after heating to cherry red 
and quenching in water, the piece bent to 180 degrees flat upon itself without fracture 
on the outside of the bent portion. The homogeneity test shall be made by nicking 
or grooving the piece under test w^ith three grooves ys oi an inch deep and 2 inches 
apart. The nicked piece is then put in a vise, and broken off above the nick by 
light blows of a hammer, the bending being away from the groove. This is to 
open up and render visible any failures to weld up, or cavities or foreign matter. 

Steel plate can be procured of any reasonable length, since it origi- 
nates from an ingot which can have the necessary weight to give 
both width and length. Plate is stronger in the direction in which 
it has been rolled, than at right angles to this axis. Hence it is 
better to make up the length of the shell by several rings than to 
make fewer ring seams and more longitudinal by using the plate the 
other way. In Fig. 11 is a design made up of the two heads, the 
dome piece and its head and one sheet to form the cyHndrical portion. 
Such boiler can have only the circumference imposed by the greatest 
distance between the housings of the rolls by which the plate was 
made. This is in the neighborhood of twelve feet in the largest mills. 

In former years badly chosen or improperly treated steel gave 
trouble by cracking along the rivet holes, and this could only be pre- 
vented by troublesome and costly annealing. It is no longer liable 
to occur in good material and with the rivet holes drilled or reamed 
effectively. 



32 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



28. Shaping the Shell Elements. Curving Plates. The plates for the 
cylindrical part of a boiler shell of large diameter will be received flat from 
the manufacturer, and must be bent into the cyhndrical shape. This 

is done by rolling them 
cold between three driven 
rolls, so arranged that as 
the plate is moved and 
driven by two of them 
it shall be continuously 
pressed by the third 
and caused ' thereby to 
receive a continuous cur- 
vature. Such rolls are 
called bending-rolls, and 
may be arranged with 
their three parallel axes 
horizontal or vertical. 
The horizontal arrange- 
^ ment is much preferred in 
^. America by reason of its 
S convenience (Fig. 12). 
The three rolls may be 
arranged relatively to 
each other in two ways. 
Two of the rolls may be 
fixed in position, both 
driven by power and with 
their axes in a horizon- 
tal plane; the third 
will lie above the space 
between the other two, 
or with its axis in the 
plane of the common 
tangent to the other 
two. This third roll 
will be the bending-roll, 
will have its axis adjustable, and will not be driven. Its position 
further from the lower rolls or nearer to them will determine the radius 
of the curvature of the plate (Fig. 13). The rolled and curved plate will 
gradually enclose the upper roll, so that if the bent edges are to come 
together the bearing or housing of this upper roll must be removable at 
one end to allow the completed cyhnder to be removed endwise (Fig. 12). 




THE BOILER 



33 



This arrangement of rolls does not cause the plate to be curved all the 
way to the edges which are parallel to the axis of the rolls, since a 
distance equal to the radius 
of the roll or more cannot 
receive the curving action 
of the upper roll with large 
diameters of cy Under (Fig. 
13). A modification is to 
arrange the two driven rolls 
over each other, and to 
make the third approach 
the opening between them 
at an angle from below 
(Fig. 14). This arrange- 
ment brings the curving 
effect close to the edges, 
and has the plate positively 
driven against the bending- 
roll by the nip of the two 
rolls which are driven. The 
only difficulty arises from a 
change of lengths of the 
contact surface as the cyhn- 
drical shape is developed. 
The two driven rolls would 
develop equal lengths as 
they revolve without slip- 
ping upon the shorter inner 
surface and longer outer 
surface of the curved plate. 
If this were not overcome, 
the driven rolls would exert 
a calendering action on a 
plate of sensible thickness 
and undo the curving effect 
of the third roll. The diffi- 
culty is met by driving one 
of the two rolls from the 
other by a differential or 
" box " gear, by which the 

motion reaches the second roll from the first through a couple of pairs 
of bevel-wheels. The axes of one pair are independent of the fixed 




34 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

frame, so that if one roll has farther to move than the other the differ- 
ence in path is able to be compensated by a motion of this movable 
axis which allows the gears to roll through a space while still trans- 
mitting the full driving effort necessary. 




Fig. 13. 

The rolling process is effected by rolling the plate back and forth 
through the rolls with continuous adjustment of the third or bending 
roll until the gauged diameter of the cylinder or segment of cylinder is 
reached. The rolls have to be of diameter sufficient to withstand the 



B— 




& — :E' 



Fig. 14. 



tendency to flex, and of length sufficient to handle the longest or widest 
plate used. The rolls limit also the thickness of plate convenient for 
shells. Their convenient diameter imposes a lower limit for the diam- 
eter of flues to be made by their use. Their length imposes a limit 
upon the length of boiler shell to be made in one piece, or in two 
pieces if the joint is to be longitudinal. 

29. Arrangement of Rings of Plate in Shells. It is desired to have 
as few joints in the shell as possible, and yet the boiler must have a 
practical length. The least number of joints is reached in the arrange- 
ment shown for a shell boiler in Fig. 11, where the shell part is one long 



THE BOILER 



35 



plate joined lengthwise. The size of such boiler is limited by the 
attainable size of single sheet both as to length and diameter, so that 
it is much more usual to arrange the length of the plate circumferentially 
and to get the necessary length by jointing such rings or zones by one, 
two, or more ring seams. In very large diameters, such as are usual 
in marine boilers, the rings themselves will each be made up of two 
or more segments, jointed by longitudinal joints. (Fig. 100.) In the 
ordinary shell of stationary practice the ring or zone is in one piece, 
joined at the edges, and the usual diameter of such shells is fixed by the 
length of plate usually to be had. If there are three such rings or belts 
as in the usual iron boiler and in man}^ steel boilers, these rings may 
be jointed to each other at the roundabout or ring seams in one of three 
ways. The three rings may be true cylinders, each a little smaller than 
the preceding, so that they fit inside successively like the joints of a 
telescope, and the larger laps over the smaller one (Fig. 112) ; or one ring 
may be smaller than the other two (usually the middle one smaller than 
the two end ones), so that it will fit inside of both and form a lap 



R R R R R 


rrrr n~ ^r^r^ 


T 
Y Y fr)\ Y Y 


rr Vii= ^ D 



Fig. 15. 



(Fig. 15, 69, 70, 73, 134, and 188). The third plan is to taper each ring 
shghtly, so that it will fit outside at one end over the end of the next 
ring. This end has the same diameter as the small end of that same 
ring, so that the two ends of the boiler are of the same diameter. The 
taper of the rings is laid out so that currents of hot gases or flames 
shall not impinge against the ends of such lapping ring joints, but 
shall flow over the ridge which the lap makes. (Fig. 84.) 

30. Shaping Shell Elements. Flanging Heads. The head of the 
boiler shell is that flat or arched surface which closes the two ends of the 
cylinder. It has to be jointed to the cylindrical portion. American 
practice is to have the cyhnder fit over the outside of the head, and to 
bend up the edges of the head all around to form a surface parallel to the 
cyHndrical shell by which the joint can be made. This bending up of 
the edges of a flat disk to form a projecting ring or flange is called 
" flanging." It may be done by hand or by machine. By hand the 
edge is heated locally, a sector at a time, and the hot metal is bent over 



36 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

the edge of a properly moulded anvil or former by means of heavy 
wooden beetles or mauls in the hands of skilled strikers or smiths. 
Wooden heads do not draw down the metal in bending as metal sledges 
would, and the blow is delivered over more surface. The objections 
to hand-forming are the cost of labor, the impossibility of uniform 
heating all round the edge, and the inaccuracy of the final cylinder. 
Steel heads, forge heated and hand flanged, must be annealed after 
forming, since steel is specially sensitive to inequalities of heating, and 
the finished head unannealed is all distorted and unequally strained 
from this action. Hand flanging must be so done that the steel never 
cools under treatment to its critical temperature, which is found at 
about a blue heat. It is brittle and liable to crack under the blows 
of even the wooden mauls. 

Machine flanging is much to be preferred where practicable. It is 
usually a process of hydrauhc forging with proper dies. When done 
at one process two cast-iron formers are used, one male and one female. 
The disk is heated uniformly all over, and when at proper temperature 




Fig. 16. 



is laid upon the top of the hollow female die. The male die descends 
concentric with the other by hydrauhc pressure, and forces the plate 
to bend up uniformly all around and take the shape of the standard 
male former. The head is thus shaped at one heat to the required 
shape and diameter without distorting strains. In other forms of 
flanging press (Fig. 16) the plate is held at a proper temperature between 
the faces of the hydraulic vise, while pressure comes radially upon the 



THE BOILER 37 

edge of the disk from hydraulic cyHnders which carry shaping heads 
and bend down the edge gradually until the disk fits the former, which 
is the face of the hydraulic vise. 

■Earher European boilers will show the head jointed to the shell by 
a ring of angle-iron section, or by a ring of plate forged into that shape. 
The use of more ductile and superior metal for heads has made flanging 
more usual. 

The flange is usually placed inside the boiler. This keeps it protected 
from the rapid oxidation or burning to which projecting flanges would 
be exposed if hot gases or flame impinged on them and they were 
only cooled by conduction from the water at some inches' distance. 

Flanging stretches the metal right at the bend, but compresses the 
metal beyond the bend which forms the flanged surface. The sharper 
the angle of the bend, the more severe these concentrated strains. 
Hence to bend flanges with a radius not less than four inches has been 
specified, to diminish this source of trouble. Flanging is also necessary 
in jointing rectangular fire boxes and for the attachment of large flues 
to boiler heads. 

31. Joints in Boiler Shells. Welding. The rings which form the 
cylindrical shell of the boiler are curved from flat plates, and must be 
jointed at the edges and at their ends. The requisites of such a joint 
are: (1) strength to resist the strain from internal pressure; (2) tight- 
ness against leakage of water or steam, with a construction which shall 
not be too costly; (3) ability to withstand heat; (4) ability to undergo 
changes of shape from expansions and contractions without injury 
to the metal. 

The two edges of the plate which are to be joined are arranged so 
as to lap over each other to be secured together, and this attaching 
can be done by welding or by some form of the rivet joint. Bolting 
with a thread and nut will not meet the second requirement of tight- 
ness against leakage unless the joint surfaces are planed and finished 
and the bolt holes reamed and the bolts turned. This is prohibitory 
from its cost; and even if this were not a barrier, the friction of the 
nut so reduces the clamping power of the screw bolt that it would 
make a much weaker joint than is secured by the other plans. 

Welding of boiler plates to make the joint with itself or other 
parts of the shell offers many advantages. The welding property of 
wrought iron and ductile steel enables them to unite at clean sur- 
faces when pressed together with sufficient force in a state of suffi- 
cient plasticity from heat. The presence of oxide of iron or dirt or 
cinder between the contact surfaces will prevent a, satisfactory weld, 
or if there is no adequate pressure to unite the surfaces together. 



38 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

When welding is satisfactory it may be expected to be as strong as 
the rest of the metal — which has, in the case of wrought iron, been 
fabricated into plate by availing of the welding property through 
the entire course of manufacture. 

Welding of plate is done by lapping the two edges over for two 
or three inches, heating the lap to a welding heat on both sides by 
a flame or jet of gas free from sulphur or other oxidizing tendencies, 
and then bringing the lapped surfaces together either by the force 
of percussive hammer or sledge blows or by steady pressure of cams 
or roller presses. Some fluxing material like borax which will make 
a fluid glass with oxide of iron may be used as a protection for the 
contact surfaces, so as to prevent oxidation from exposure to air, 
with the expectation that it will be expelled from the joint by the 
welding pressure, and carry with it everything which would inter- 
fere with good welding. 

Welding of boiler joints offers these advantages: 

(1) It makes the joint as strong as the rest of the plate, or nearly so. 

(2) The plate is no thicker at the joints than elsewhere. This 
avoidance of a lap keeps the tensile strain from internal pressure 
always in the axis of the plate and without a tendency to flex at the 
lap or joint (paragrafs 32 and 196). 

(3) Double or extra thickness is avoided at laps or joints. The 
plate gets unnecessarily hot at multiple thicknesses, and oxidation 
is more rapid there. 

(4) No rivets are required, which makes the boiler lighter and 
less liable to leak. 

(5) A good welded seam is water-tight and requires no calking. 
The objections to the welded seam in boilers are: 

(1) It cannot be inspected for its satisfactory quality unless it is 
so bad as to allow water to leak through it under pressure. But it 
may be water-tight and yet be far from having full strength. While 
a test by hammer taps to observe the resonance of the metal at the 
joint will reveal much to the practiced ear, it lacks the convincing 
force of an inspection of each single rivet in a riveted seam. 

(2) Welded joints in large shells can only be gotten from a few 
firms with facilities and experience for such work. This has some 
effect upon the cost of such joints. But when a satisfactory welded 
seam can be obtained it makes an ideal joint. 

In cylinders with closed ends the last seam must be riveted even 
if the others are welded. The exception is where the head is flanged 
outward, or is convex inward so as to bring the closing joint outside 
the shell (paragraf 60). 



THE BOILER 39 

33. Riveted Joints for Boiler Shells. When two plates are to be 
joined by rivets, they are lapped over each other, and through a 
hole which matches in the two plates a rivet is introduced red or 
white hot. This rivet has a head formed at one end in its manufac- 
ture, but the shank is straight. When in place through the holes, 
pressure is brought upon both ends of the rivet, whereby the project- 
ing shank is upset and forced back upon itself, thereby enlarging its 
diameter in the hole until it fills it completely, and when the metal 
can no longer be displaced laterally in the holes, the metal of the 
rivet still projecting beyond the plate, spreads sidewise over and 
beyond the hole and forms the second head of the rivet. The rivet 
when completed has two heads connected by the shank which is still 
red hot when the head is finished, and which, in its contraction on 




Fig. 17. 

cooling draws the two plates together with a force measured by the 
modulus of elasticity of the rivet metal and by the cross section of 
the shank. It is a force much in excess of that which any bolt and 
nut can exert. 

The riveted joint meets the requirements of a boiler joint in that 
it is 

(1) .Strong. 

(2) Water-tight. 

(3) Cheap. 

The difficulties which it introduces are 

(1) The hole for the rivet cuts out just so much metal from the 
solid plate, and therefore the joint is not as strong as the plate where 
there are no holes. 

(2) In simple lap joints the strain on either side of the joint is 
not resisted in the axis of the plate on the other. High pressure 
tends to flex the lap joint till the two plates come into line (Fig. 17), 
and this flexure causes the deterioration called '' grooving " (para- 
graf 196). 

(3) The boiler shell is thicker at joints than elsewhere. 

There are certain further disadvantages attending a badly made 
rivet joint which will be noted hereafter: The design of special 
riveted joints is to diminish these diflftculties. 



40 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

33. Construction of a Riveted Joint. Punching and Drilling. 

The holes in the plate to receive the rivets may be made by punching, 
by drilling, or by punching out a small hole and enlarging it by 
reaming. Formerly, and with iron plate, punching was universal. 
More recently, and with steel, the latter methods are used. 




Fig. 18. 



The punching of the hole is done in a punching press (Fig. 18) 
in which a hard and tough steel cylinder comes down upon the 
plate supported upon an abutment or female die having a hole in it 
slightly larger than the punch (Fig. 19). The punch shears its way 
through the supported plate and extrudes a blank of the punched 
plate cut by its stroke. While at first the punch cuts the plate, after 
a fraction of an inch of penetration it tears its way through the rest 
of the thickness without true shearing action; and in a plate of 
laminated structure such as wrought iron has, it is largely the reac- 



THE BOILER 



41 



tion of the abutment or die which Umits the lateral spread of the 
tearing effect. The extruded blank is conical, since the die is larger 
than the punch in order to free the latter and pass the blank.* The 
punching presses may be crank presses as shown, or the punch may 
be driven by hydraulic pressure. Flanged plates are usually punched 
in horizontal punching presses. A spiral shape has been given to the 
impact face of the punch so as to make the cut a gradual and pro- 
gressive one around the circumference of the hole, and to help secure 
a true shearing action (Fig. 20). 

Drilling of plate is done by the ordinary machine shop drill of two 
cutting planes meeting at an edge. Twist drills are most convenient, 
although the flat drill is still to be met. The drill will be run by the 
ordinary drill press. 

The gang punch or multiple punch has a number of punches mounted 
in a fixed relation in a holder, so that one stroke of the holder punches 
two, three or more holes at once and at a standard distance apart. 

Gang or multiple drills have a number of revolving spindles driven 
from a common source, each carrying its own drill and drilling a number 




Fig. 19. 



Fig. 20. 



of holes at once and at a fixed distance apart. These gang drills usually 
drill alternate holes in a seam to permit a convenient distance between 
the spindles. 

34. Punching and Drilling Compared. The objections to punching 
the holes for the rivets are: 

(1) The injury to the plate. The impact-pressure of the punch 
upon carbon steel produces an effect upon the metal around the hole 
similar to that of hardening by heating and rapid cooling. The metal 
has its modulus of elasticity raised, so that it stretches less before 
breaking or cracking, which is the same as becoming brittle and hable 
to fail in service under strain suddenly applied. Experiments would 

* Usually larger by -^^ the diameter of the punch. 



42 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

appear to show that the carbon of the steel enters into combination with 
the iron under the shock, and, to restore the metal to the normal 
ductihty after punching, the plate must be annealed. Otherwise the 
deteriorated metal must be removed by the reaming or enlarging of the 
hole until good metal is reached at a distance from the punched place 
beyond the effect of the blow of the punch. 

(2) The spacing of the holes is likely to be inaccurate in punching 
with a single punch, and when punched independently the holes in the 
plates which lap will not match, or will be ''half blind" (Fig. 21). 
This difficulty arises when massive plates are presented by hand to the 
punch and the work is done too rapidly. The holes are laid out or are 
marked on the plate, and the punch mechanism thrown into gear when 
the mark is under the axis of the punch. Even when the punch has a 
'' tit " (Fig. 19), to serve to guide it to the axis of the hole it may seem 
to take too long to adjust the plate, and the stroke may be made before 
the setting is perfect. Gang punches avoid this trouble so far as 
each set is concerned, but best results are had from the use of feeding 
tables on which the plate rests, and which are fed forward by racks or 
similar feed devices, so that the plate moves each 
^ ^^^R time through the same fixed distance, thus securing 

\^^ \ l^p\ uniform spacing of the holes upon a line. Errors 

^ ^H) may creep in even here from a divergence laterally 

of the lines of holes which are accurately spaced 

lengthwise in two plates. Inaccurate spacing which 

causes the holes to come half blind to each other 

must be corrected either by reaming out the holes 

Fig. 21. till they do match, or by stretching them by the 

drift-pin to be referred to hereafter (paragraf 43). 

If they do not match at all, the two holes are blind. 

The objections to drilHng the holes are: 

(1) With the single drill the process is slow. It takes from five to 
seven times as long to drill as to punch, or five or seven holes can be 
punched while one is being drilled. 

(2) This makes drilling costly unless gang methods are used. 

(3) The point of a drill is not a true point, but an edge where two 
cutting planes meet. Hence the drill in starting has a tendency to 
work sidewise away from the true axis of its hole and follow one or the 
other of the corners of the edge plane. If this tendency is disregarded, 
the holes do not come true except by accident. If time is taken to 
keep the drill starting true, the work is slow. 

(4) A drilled hole in thin plate usually has a burr or projecting ridge 
raised around the edge of the bottom of the hole, where the feeding 



THE BOILER 43 

pressure on the spindle and drill forces the latter through the thin film 
of metal which remains in the hole after the point of the drill has come 
through, and cutting and resistance is at the edges only. This burr 
would prevent the joint of plates being water-tight unless it was carefully 
removed by fiUng. 

(5) The drilled hole is cylindrical; the punched hole is conical. It 
is an advantage to have the hole conical if the two small bases of the 
cones can come together (as at B in Fig. 31). The sloping sides give 
greater holding power to the head, and give a form of rivet better calcu- 
lated to prevent the head from snapping off in service. 

The points in favor of punching are its rapidity and cheapness. The 
points in favor of drilling are its harmlessness to the plate and the 
probable greater accuracy as to the matching of the holes. 

The plan of punching small and enlarging to size by reaming out the 
holes offers the advantage of rapidity and cheapness, and leaves no 
deteriorated metal. One-tenth of an inch of metal cut away from the 
edge of the hole will remove the hardened material, and such reaming is 
much more rapid than driUing out the soUd metal. The reamer may 
be tapering if conical holes are preferred. A great deal of work is 
done by this method, as combining the commercial advantages of one 
and the advantages as to quality offered by the other. 

Drilling, however, must be exacted for thick plates and large holes, 
and is best at all times. In the very highest standard of practice it is 
further exacted that the holes shall be drilled after the plates have been 
curved and assembled, so that the holes shall be drilled truly radial in 
both plates and with the sheets in place. This prevents troublesome 
burring, and prevents mismatching of holes. Special machines have 
been erected for this grade of work. 

35. Hand- and Machine-riveting. The pressure necessary to upset 
the shank of the rivet into the rivet-hole so as to fill it and to form the 
second head can be exerted either by hand-hammers in the hands of 
skilled riveters, or a die or swage may be put over the end of the shank 
and struck by heavy sledges so as to upset the shank and develop the 
form of the die on the projecting end; or the pressure can be brought 
upon the rivet by a machine called a riveter or riveting machine. 

In hand-riveting, the rivet is pushed up from within wherever possible, 
and when in place a massive swage is held up against the inner head of 
the rivet by a helper with all the force possible, by leverage, while rapid 
blows are delivered upon the end of the hot shank by the riveters with- 
out. Hand-riveting is necessary for the closing seam of a shell in order 
that resistance to the heading of the rivets may be offered from 
within, and by the riveters' helper with his swage. The design of the 



44 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

shell must be such as to allow the '' holder-up " of the swage to get out 
of the boiler when the seam is completed. But machine-riveting gives 
so much better results in filHng the holes by upsetting, and in forcing 
the plates to contact before the heat comes to press upon them and draw 
them together, that machine-riveting is used wherever practicable. 
Swage-riveting with sledges is better than light hammer-work with long 
or thick rivets, but is also less effective than the work of good machines. 
The compression of the machines gives an added resistance to the joint 
by the frictional resistance which the pressure opposes to a shding of the 
two plates upon each other. This resistance adds to the shearing resist- 
ance of the rivets by preventing the shearing edges of the plate from 
commencing on the rivet until the friction is overcome. 

The usual types of riveting-machine are three: steam or air riveters, 
hydraulic riveters, and lever machines. In all types there will be a 
movable head actuated by power to compress, upset, and head the 




Fig. 22. 



rivet against a fixed abutment or " stake " which replaces the upheld 
'' swage " in the hand of the helper in hand-riveting. This stake 
requires to be a stiff and powerful organ of the riveting machine; and 
since the longer its length the more metal must be in it for strength 
and stiffness, it will be apparent that the stake Hmits either the diameter 
of flue which must pass over it, or the length of zone to the end of 
which the stake will reach; or it may limit both. The stake is fitted 
at its upper end with a die which fits the manufactured head of the 



THE BOILER 



45 



rivet (or else will reshape it), and the rivet is pushed through the hole 
from the stake side. The movable head is then allowed to exert its 
force endwise upon the rivet, upsets and heads it, and is then retracted. 
The steam-riveter shown in Fig. 22 has a piston of large area, which 
receives a relatively light pressure of steam or air upon each square inch 
of area, so that the necessary aggregate force is secured. The exhaust- 
steam after the working stroke comes round also to the front side, and 
is exhausted first from the working side so as to leave a pressure to 
retract the piston before the exhaust occurs' from the front side. The 




Fig. 23. 



hydraulic riveter uses a plunger of small area, exposed to a water- 
pressure of considerable amount, perhaps 250 to 350 pounds or more 
per square inch, so that a much less area under greater pressure does the 
same work as the large area under less pressure (Fig. 23). The lever 
or press riveters have an elbow-joint linkage which hangs flexed when 
the movable head is at rest, but can be straightened out by means 
of a cam or a third link, and in its straightening it compresses the 
rivet in its place against the stake with the great force of the elbow- 
joint combination (Fig. 24). Some portable riveters are constructed 
on this principle with a fluid acting upon a piston to cause the elbow- 
joint links to straighten. Such are much used in bridge-shops and 
for girders. 

The hydrauhc riveters are the most compact, but the high pressures 
used in them give trouble at the packings. They move more slowly 



46 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




than the steam riveters in coming against the rivet end, and their 
effect is more that of pressure and less that of a blow. This latter 
is hard to prevent with an expanding fluid like steam, over which the 
valve exerts no control after it has been passed. Either of the fluid 
machines has the advantage over the lever machine that the pressure 
can be gradually increased to its maximum as the rivet yields and 
cools, and furthermore the pressure can remain upon the rivet an 
appreciable time. They have the further advantage over the lever 
type that the stroke or travel of the movable head is not fixed in length, 

but is fixed only by the refusal of the 
rivet to yield further to pressure. 
This is convenient when rivets of 
different length are in question for 
differing thicknesses or number of 
laps of plate. This has been met 
for the lever riveter by having 
the abutment-joint of the linkage 
mounted upon a bearing adjustable 
by a wedge for different lengths 
of rivet, or upon a yielding bearing 
which is held to its seat by springs, 
or by heavy hydrauHc pressure 
maintained by an accumulator. If 
the resistance offered by the stake to an upset of the rivet is too 
great as the linkage comes straight, the back end of the linkage yields 
and prevents such excess. It does not serve, however, if the rivet 
is shorter than the normal. Then the lever riveter does not get its 
full pressure upon the metal, while the hydraulic and steam riveters 
are not subject to this difficulty, but follow the rivet to refusal. 

The very intensity of the pressure in upsetting rivets by machine 
has sometimes caused the metal of the rivet to squeeze sidewise into 
the joint between the plates, wedging them apart and leaving a 
thin film between them. This is fatal to tightness of the seam. It 
is best to have a double ram construction, whereby an outer annular 
ram forces the two plates together as by a vise pressure before the 
inner or heading ram proper comes forward against the rivet. This 
closes the joint tight before the rivet begins to press upon it, and gives 
much the stronger and tighter joint of those made by machine. The 
use of such a riveting machine is specified by some designers. 

The riveting machines require adequate overhead hoisting appHances 
so that massive rings and shells can be rapidly and easily handled, 
and the joints and rivets presented truly in line and normal to 



Fig. 24. 



THE BOILER 



47 



This justifies a travelling crane in a 




Fig. 25. 



the motion of the heading die. 
busy shop. 

36. Mechanics of the Stress in a Thin Cylinder. The computation for the 
magnitude of the stress in the longitudinal elements of a cylinder or at the longitu - 
dinal seams of a boiler can be presented as follows in connection with Figs. 9 and 25: 

Let an element of the arc of the semicircle be denoted by dx in Fig. 25 measured 
along the tangent, and suppose its length perpendicular to the paper to be one inch. 
Then the area of that element will be 
1 X dx and the normal pressure on it Pdx. 
If this normal be decomposed into horizon- 
tal and vertical components, only that 
perpendicular to i4. 5 tends to rupture the 
joints at A and B. The horizontal compo- 
nents tend to produce rupture along EF. 
Hence the component V which is Pdx 
cos a produces the same effect as the 
force P acting over the area 1 X he, since 
he = dx cos a. Therefore the total upward 
force is the sum of the projections of all 
elements of the semicylindrical arc, or is 
equal to PD. Or, again, Pdx cos a may 
be integrated between a = + 90 and a = 
- 90, which becomes PiR + R) = PD. 
The sketch in Fig. 9 shows the reasoning 
when a solid mass like wood transmits the 

pressure to the arc just as the fluid does, and shows the rupturing force to be pro- 
portional to the diameter. This was first proposed by Forney. 

37. Copper, Cast Malleable and Wrought Iron for Boiler Shells. 
Copper is: 

1. Highly conductive of heat. 

2. Easily molded with light machinery. 

3. Resists corrosion from water and gases. 

4. Scale does not adhere to it as to steel. 
On the other hand it; 

5. Has a low tensile strength, and must be thick. 

6. Is costly to buy as compared with steel. 

7. Loses its tensile strength as it gets hot. 

8. Sets up galvanic action in acid waters with other metals. 

9. Is liable to mechanical injury from fire tools. 
Brass is the same as copper. 

Copper has been used in some locomotive fire boxes and for ferrules in tubular 
boilers. 
Cast iron is: 

1. Cheap. 

2. Easily molded by casting into shape. 

3. Rivets are not required, as units will be made in one piece. 

4. Less liable to corrosive effect of gases. 
On the other hand it: 

5. Has low tensile strength ; hence has to be thick. 



48 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

6. Is not ductile, but is brittle, and breaks without yielding. 

7. Is liable to blowholes or defects below the surface. 

8. Is liable to lines of weakness at corners due to unequal cooling. 

9. Repairs after breakage are troublesome. 

No. 7 is the prohibitory defect, when the metal is liable to sudden changes of 
temperature. Cast iron is prohibited in Great Britain where it must withstand 
pressure and is reluctantly insured in the United States. Its thickness made it 
popular where fittings were to be screwed in, as the thread would be long enough 
to be tight. 

Malleable iron is used in fittings and parts of special boilers. Its objections are: 

1. If malleableizing process is not complete the material is variable and unreliable 
exposed to heat and stretching. 

2. Its coefficient of expansion by heat is not the same as steel or wrought iron. 
Wrought iron is hard to get under modern manufacture except in tubes. Old 

classes were: 

1. Tank iron. | :-.-.-.-.-.v.v.v7.--.v.v. •■•■•.••.•••■••••••••• 

2. Shell iron. | 

3. Charcoal No. 1. X >^ - ^ = 

4. Charcoal-hammered No. 1. ^^^..^^^^^^^^^ 

5. Flange iron. 

6. Fire-box iron. Fig. 26. 
It was made by welding, piling, reheating 

and welding the pile until the cinder was mechanically expelled and a plate built 
up of required quality. Such material was liable to blisters or lamination due to 
defects in welding and from pockets or threads of cinder. These made bags or 
blisters in the shell under localized heating, which were elements of Weakness and 
danger (Fig. 26). 



CHAPTER III. 

BOILER RIVETING, STAYING, AND STRUCTURAL DETAILS. 

40. The Mechanics of the Riveted Joint. Efficiency. The theoreti- 
cal design of a riveted joint would involve giving to the thickness of 
the plate (t) and to the diameter and cross-sectional area of the rivets 
{d and a) such values that when the rivets are spaced at a distance 
apart from each other called the pitch (p) measured from center to 
center, the required strength was secured with the unit stresses in rivet 
and plate within safe limits, and equal to each other in each element. 

The superior limit of the strength of the joint is the unperf orated 
plate, or the strength of the metal between holes. The efficiency of 
a riveted joint is the ratio which the highest allowable stress in such 
completed joint bears to the unperforated plate. The ideal is to have 
the efficiency in detail of the tension on the plate, the shear of the rivet 
and its resistance to compression in bearing upon the side of the whole 
equal to each other. 

If a force in tension F be transmitted through a single riveted lap joint such as 
Fig. 32, the net area of the plate is (p — d) t. If the tensile resistance be denoted 
by /, then for the plate Ft = tf (p ~ d) and the efficiency 

(p-d)tf V- d 

tjt = J— = . 

fpt p 

For the bearing area of the rivet in compression 

F = dtC 
when the compression resistance is C and the efficiency 

_dtC _dC^ 
'~ ptf ~ pf' 

For the rivet in shear, the stress is 

F = 1 Tzd^S, 
and the efficiency 

These can be solved in any case by assuming a value for the tension and com- 
pression stresses, say 55,000, and for the shearing resistance, say 45,000, and dimen- 
sions for the pitch, rivet diameter and plate thickness and solving. The lowest 
value for E is the efficiency of the joint as a whole, and in the ideal case are all equal 
to each other. If the double riveted lap joint is used there is additional rivet area 
for bearing and shear introduced and in triple joints still more with increased 
efficiency of the joint and the equations can easily be written for each case. The 

49 



50 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



butt joint by eliminating the cross bending of the two plates at the joint adds 
strength and efficiency, particularly when double or triple riveted. Usual values 
for the efficiencies are: 



Single riveted lap. . . 
Double riveted lap. 
Triple riveted lap. . , 
Double riveted butt 
Triple riveted butt. 



Fig. 32 
Fig. 33 
Fig. 34 
Fig. 35 
Fig. 36 



Per Cent . 



55 
70 
75 
80 

87 



Figs. 17 and 30 illustrate the flexure which double butt-joint designs are intended to 
remove. They diminish also the danger from grooving the plate at the joint, to be 
discussed hereafter under corrosion of the plate. 

The tendency of large diameter rivets is to lower the area of the unperforated 
plate: small pitches have the same effect. The boiler joint requires to be water-and 




steam-tight as well as of best allowable strength. The following tables give data 
upon lap and butt joints from the practice of the Hartford Steam Boiler Inspection 
and Insurance Company and shows proportions which they recommend. 



TABLE V. DOUBLE AND TRIPLE RIVETED LAP JOINTS. 



Thickness 
of Plate. 



Diameter 
of Rivets. 



Pitch of 
Rivets. 



Distance Be- 
tween Rows of 
Rivets. 



Edge of Plate 

to Center of 

Rivets. 



Pitch of Girth 
Seam Rivets. 



Efficiency of 
Jointi 



Double Riveted. 















Per cent. 


i 


H 


2| 


111 


li- 


2^ 


74 


A 


f 


2| 


lit 


lA 


H 


72 


1 


i 


3i 


2i% 


m 


2f 


70 


A 


if 


3i 


2^ 


n 


2^ 


70 


i 


1 


3f 


2i 


m 


2h 


68 



Triple Riveted. 



i 


f 


3 


2 


lA 


2^ 


77 


A 


^ 


3| 


2^ 


H 


2i 


76 


, 1 


1 


3i 


2A 


1^ 


H 


75 


^ 


1 


31 


2i 


iM 


2f 


75 


i 


^ 


m 


2f 


H 


2i 


75 



BOILER RIVETING 



51 



TABLE VI. DOUBLE AND TRIPLE RIVETED BUTT JOINTS. 



Thick- 
ness of 
Plate. 



Diam- 
eter of 
Rivets. 



Pitch of 
Rivets. 



Width of 
Outside 

Butt 
Strap. 



Width of 
Inside 
Butt 
Strap. 



Thick- 
ness of 
Butt 
Straps. 



Dis- 
tance 
tween 
Rows 

of 
Rivets. 



Edge of 
Butt Strap 
to Center 
of Rivets. 



Pitch 

of 

Girth 

Seam 

Rivets. 



Effi- 
ciency 
of Joint. 



Double Riveted. 





















Percent. 


^ 


H 


2\ X4i 


4i 


9 


i 


2i 


n 


H 


83 


1 


1 


2f X4f 


4| 


91 


T^ 


2t^ 


u 


H 


83 


A 


i* 


2MX4if 


5i 


m 


■i 


2| 




2i 


82 


i 


1 


2^X5i 


5f 


Hi 


-h 


m 


m 


2i 


80 



Triple Riveted. 



1^ 


H 


3iX6i 


9i 


14 


1 


2^ 


1. 


2t^ 


88 


f 


1 


3iX6i 


9i 


14i 


1^ 


2iHT 


1^ 


2^ 


87.5 


1^ 


I 


3fX6f 


lOJ 


15f 


t 


2i 


IM 


2i^ 


86 


i 


H 


3fX7i 


11 


16f 


A 


2| 




2i 


86.6 



A considerable addition to the initial strength of a riveted joint, particularly when 
machine riveted, is given by the pressure of the plates upon each other and the 
friction between them. When the rivet head is quickly formed and the metal upset 
in the hole while still essentially red hot the shank in contracting draws the plates 
together with great force. This force must be overcome by a slipping of the plates 
over each other before the rivets begin to shear or the plate to tear. Experiment 
has shown that the shipping load for rivet on a double-riveted plate with f -inch rivets 
was 7 tons and with 1-inch rivets from 8 to 10 tons and over twice that required 




Fig. 31. 



when the same joint was hand riveted. With the factor of safety of 6 referred to 
above, these slipping loads should not be reached in service. After slip has once 
occurred, however, and in old joints which have been loosened by flexure or corrosion 
of either plate or rivet, this extra strength can no longer be counted on. To give 
effective contact area for the plates and to leave plenty of sound metal outside of 
the holes both for strength and tightness, the first row of holes is usually put at least 
one and one-half times the hole diameter from the edge of the plate. 

41. Arrangement of Rivets in a Joint. Special Joints. Fig. 31 
shows the conventional types of rivet in section. A has the conical 
head made by hand, the bottom showing the usual pan tail which the 



52 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




Fig. 32. 




Fig. 33. 



BOILER RIVETING 



53 



rivet has as manufactured. B is the cup or button head resulting 
from the use of a swage. C or A will represent forms given by the 
dies of riveting machines. D is the countersunk head usual in ship 
work or where a smooth skin surface is to be sought. 

Rivets of iron boilers should be of iron, and for steel boilers they should 







Fig. 34. 

r^ /^s r^ c^ r^ r^ 



^ \y 



^^ 



Ml 



LE 



V V V V 



y^^ 



^^ 


^-^ 


r-\^^ 


f^' 






























1 \^J) 







Vi^y ' 






(1^ 






/^ 




1 ^-^ 


('~'^) 


('' '') 








y^^j 






W.') 






w 


W 






\(CD 




O 


(C.=) 




(n)i 




r'M 


/r~\N 








^— \ 










1 


(v /) 


iv ;) 


/ — ^ ' 






(( "M 






(f^ 




' (^ 






v^' 






v^y 






v^ 




ikJ) 


a 


(O) 


^1 








0) 


© 






i@ 




@ 


© 




b 


O 


© 


© 


© 


© 



Fig. 35. 



Fig. 36. 



be of a mild steel able to stand the proper forge tests. Their tensile 
strength is usually taken the same as the shearing strength (or ^^ of it), 
and may be put at 55,000 pounds to the square inch for steel. The 
forge tests are; 



54 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

(1) Bend double close when hot. 

(2) Bend to a U over a bar of its own diameter cold, and show no 
cracking in either case. 

(3) The head should hammer hot to form a disk 2h times the diam- 
eter of the shank. 

(4) The shank should hammer cold to a flat i of an inch thick, and 




Fig. 37. 



H^^3;.Ju4t-3JJH-3-'*k--3-'4«-3-^J*-3'-4--:^->^-3->< ' — ' ^ 






S 




l_Li_: ---^-^ -T— -1 ■ \ 

fO-i O— r— ^ ^- — -^-v-^- 



^4 



■Oh-. 



<|>J1-— '-4- 



^_ 






Fig. 38. 




then withstand punching with a solid punch, making a hole of the 
size of the original shank; both of these without cracking or splaying 
at the edges. 



BOILER RIVETrNG 55 

>^ 

For wrought-iron rivets the tensile strength may be called 50,000 
pounds per square inch, and the shearing strength 40,000 pounds; the 
metal should withstand the same forge tests. 

The arrangement of the rivets in a boiler joint will be either ordi- 
nary or special. The ordinary riveted joints are presented in Figs. 32, 
33, 34, 35, and 36. 

In chain riveting the two rows are one behind the other in Hne (Fig. 
35): in staggered riveting the intermediate row is placed opposite the 
spaces in the other two (Figs. 34 and 36). The triple-riveted joint 
(Fig. 34) gives a longer lap and more plate area and more rivet-shearing 
area, as well as a stiffer joint. The butt joint with double cover (Fig. 35) 
doubles the number of rivets required as compared with the same 
class of lap joints, but the strain is in line and without tendency to 
flex the plates, and the rivets are in double shear. It is not so with 
the butt and single cover (Fig. 30). The double-cover butt (Figs. 35 
and 36) is Hable to have the outer cover overheated when exposed to 
fire. The special joints are departures from the four conventional 



L 



A 



^"1#!^M^1^ 



riv4twt 



^m 



■m- 



^ 



SECTION_AT A-B 



\^j y y v^ y y V ^4. 



#T^ 



m 



m® 



% 



(Sy^ 



m 



4) 



m^ 



® 



m) 



<§) 



m^ 



!^» 



% 



'■m^ 



4) 



% 



m-^ 



Fig. 39. 



types, seeking to secure the advantages of the double butt with greater 
or less expense. Figs. 37, 38, and 39 will serve as types of such joints. 
The strength of single lap joints being from 55 to 60 per cent of the 
original plate, and of double riveted laps 70 per cent, such special 
double butt joints as Fig. 38 will show a strength of 85 per cent of the 



56 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

solid plate. The joint of Fig. 39 with || rivets in one-inch holes in 
f plate would be called a quadruple riveted butt joint and has an 
efficiency of 93.5 per cent. 

43. Failure of the Riveted Joint. While the riveted joint fails in 
one of two generic ways, either by shear of the rivets or by failure of 
the plate, the latter may occur in several ways. The rivet may (c) 
buckle or (e) shear the plate in tearing its way out, or the plate may 
crack and tear (6) either between rivets or {d) between the rivet and 
the edge of the plate. The excess of rivet area to secure tightness for 
the seam usually makes the failure occur in the plate (Fig. 40). The 
danger from (c) occurs when hard steel rivets are used in soft iron plate; 
(e) may happen when the Hne of rivet holes is too near the edge of the 





Fig. 40. 



plate and the rivets are hard and dense. It is the least usual. The 
failure (b) is most common. The line between rivet holes along the 
pitch is the shortest line or line of least resistance, and any maltreat- 
ment of the plate in making the joint has tended to make it weaker. 
Such maltreatment may come from punching without reaming or 
annealing, whereby the steel is more brittle and less tough than it should 
be (paragrafs 27 and 34) ; or if the use of the driftpin has been per- 
mitted, the metal has been initially strained locally thereby beyond 
its elastic limit. 

43. The Driftpin is a tapering pin of hard and tough steel which is 
used to force and draw into coincidence two holes in a seam which have 
not come opposite to each other. (Fig. 21.) The taper pin is inserted 
in the half-bhnd holes and driven downward, so that it wedges the pro- 
jecting edges of the holes over and draws the metal around the holes out 
of shape until the distorted holes agree. This will buckle the metal in 
front of the hole if the error in alignment is at right angles to the pitch, 
and cause failure (c), as well as strain the metal along the line of the 
pitch and start the crack which ends in failure (6). If the error in 
alignment is along the line of the pitch, the driftpin tends to start 



BOILER RIVETING 57 

failure (d) and injures the plate between rivets, which renders it hable 
to failure (6) also. The driftpin is fatal to good metal in steel boilers, 
and its use should be forbidden by the specifications. If holes must be 
expected to be inaccurately spaced, the coincidence should be brought 
about -by use of a cutting reamer, whereby no injury to the material 
is incurred. DriUing the holes in place makes both drift and reamer 
unnecessary. 

The failure of the joint by gradual action of overpressure by methods 
(c) and (e) is apt to show itself by leakage before it is imminently 
dangerous. Inspection may also reveal failures {h) and {d) if they are 
not the result of some sudden strain. It is an element of safety in the 
riveted joint that it should give warning of its probable failure by the 
leakages which accompany the first stages of such failure. Old seams 
may fail from corrosion or grooving by other methods than these, 
determined by the character of the deterioration which has weakened 
them (paragrafs 191-6). But except where the sohd plate is weakened 
by corrosion or grooving, such wear and tear is most apt to hasten a 
failure at one of the four weak points above discussed. 

44. Stays and Staying. It has been seen (paragraf 25) that the 
sphere and the cylinder are the only forms which have no tendency to 
change shape under internal pressure. Or, in other words, that the 
circular is the limit form towards which all sections tend, and which 
they will assume if the elasticity of the material will permit such defor- 
mation of section to occur without breaking. The modern tendency 
in design is toward the use of many units of small diameter so that the 
concave or convex heads or ends of such tubular units under pressure 
shall be stiff enough without any bracing whatever. In the older forms 
of large external diameter, and particularly where the furnace element 
was placed inside the external shell, flat or nearly flat surfaces were 
numerous and their tendency to deform under pressure must be resisted 
by positive means other than the tensile or transverse strength of the 
material. Rods, bolts, bars, or braces used to prevent such deformations 
of flat or arched or non-circular surfaces are called by the general name 
of " stays.'' 

The simplest case is where two parallel surfaces, flat, or parallel with . 
one concave and the other convex to the pressure and not far apart from 
each other, are to be tied together to resist the pressure between them 
which tends to force them apart. This occurs at the sides of the fire 
box in locomotive boilers, in some marine and upright boilers, and at the 
crown sheets of some designs of locomotive boilers. The most ready 
solution is to tie the two surfaces together by round bolts or rods whose 
area of cross section shallbe sufficient to resist the pressure upon the 



58 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

area they support, and for which the distance between centers shall be 
so small that no deflection or bulging of the plates can occur between 
them. With thinner plate this center distance used to be four inches in 
locomotive practice; recent practice raises this distance to six inches or 
over. These stay bolts are either headed over hot on the outside of the 
two plates, like an ordinary hand-made rivet, or more usually the holes 
in the two plates are threaded and the stay bolt is screwed into both 
plates, and is slightly upset on the ends when in place, to prevent work- 
ing out and leaking, and also to reenforce the strength of the threads. 
Thicker plates give sufl&cient length of thread for strength. Hollow 
stay bolts are also used on the water legs of locomotive boilers, both 
because they will manifest the beginnings of failure by leakage of steam 
through the crack of the initial fracture, and because the air which goes 
through the hollow keeps them cool and helps supply oxygen for the 
fire. The simple heading of the stay bolt like a rivet was troublesome 
on account of the tendency of the shank to bend and also because an 
unequal contraction of the group of stay bolts made some too tight and 
others loose. The holes for the screwed stay bolt are tapped by a long 
tap so that both plates have their threads parts of the same screw, and 
the two plates are under equal tension if all bolts are of the same length. 
This method is most satisfactory if the stay bolts are short and of equal 
length. As they heat by contact with the steam or hot* water they 
lengthen and slack their hold, and the longer they are the more they 
yield. Hence, while this same method can be used to stay the two flat 
cylindrical heads of a C3dindrical shell boiler to each other and prevent 
their bulging outward, it is usual only for boilers of comparatively short 
length, such as are used in marine practice, or unless the pressure is to 
be so high that no other plan seems advisable. Such '' through stays " 
will be of round rods of sufficient size, threaded at the two ends, which 
have been upset so that the bottom of the thread on the enlarged ends 
shall have a diameter equal to that of the body of the rod. The hold of 
the rod in the plate by its thread is reenforced by a nut on the outside 
which caps over the end of the rod, and a flexible copper washer between 
the plate and the nut helps to make the joint water-tight. A jam 
nut on the inside with a washer helps to keep all snug, and prevents 
working loose by expansion and contraction. Since through stay rods 
of this type cannot usually be put close together, but must be spaced 
far enough apart to allow a man to pass between them for inspection 
and for work, their centers will be sixteen inches apart at least; so that 
they must each withstand the pressure in such case exerted over an 
area of 256 square inches, and it is usual to stiffen the head by means of 
angle- or channel-irons or similar structural* shapes, whereby the hold- 



BOILER RIVETING 



59 



ing power of the stays shall be distributed over the more flexible head. 
This can also be done by large washers on the outside of the head. 
Figs. 41 and 42 will show the detail of such through stays. 




Fig. 41. 



To avoid the threaded hole in the heads and the projecting end of the 
stay, the stay rod has been fastened to stay bars on the heads by a pin- 
joint. Fig. 43 shows a form of this method where the stay bars are 




t<— A->|^ A— »; 



Fig. 42. 



relatively heavy forgings of two to two and a half inches square, with 
lugs bump-welded on the inside. The stay rod ends in a fork which 
spans the lugs, and a bolt or pin connection ties the bars together upon 
the two heads. Somewhat hghter than this is the similar arrangement of 
Figs. 44, 45, and 46, where angle- or tee-irons are riveted to the head, and 
the stays pinned to them by pins in single or double shear; but in these 
arrangements the obliquity of the stay rod indicates a prevalent arrange- 
ment for medium pressures. The inner end of the stay rod in this case 
is fastened to the cylindrical shell at a convenient distance back from 
the head by rivets, and thus the bulging tendency is withstood by the 
tensile strength of the shell lengthwise, in which direction it is abun- 
dantly strong. Instead, again, of structural iron bars, single or inde- 
pendent sockets may be used, as in Figs. 47 and 48, whereby the action 



60 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




Fig. 43. 




r 



Fig. 44. 



BOILER RIVETING 



61 




/^ — 

< j 1 

< ) 


^ 


-(-) 


v= 


1 



Fig. 45. 




Fig. 46. 



62 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

of the stays is distributed even more generally over the surface to be 
stayed. Fig. 46 will serve for detail of these also. It is apparent that 
the diagonal stay must be stronger than the straight one to withstand 
the same strain (Fig. 50). The cheapest and most uncertain of the 
diagonal stays is the plain rod, flattened at both ends as Fig. 47 is at 



o 



HI 



ox 



-J.. 



Fig. 47. 

one end, and riveted by such flattened ends to head and to shell. 
Modern practice limits the use of this type to comparatively light pres- 
sures, and prefers the form of molded steel forged up without welding 
from steel plate to the welded types. Fig. 49 shows some of these forms. 
Such stays are strong as they approach paralleHsm to the shell for they 
must withstand a stress which is related to the straight or normal pull 



BOILER RIVETING 



63 



on the area which they support, as the length of BC in Fig. 50 is 
greater than AB. 

Gusset-stays are a form approved for heavy pressures. Triangular 
or trapezoidal pieces of boiler plate are riveted to angle irons on the 
head and cylindrical shell and bind them into a rigid structure or the 
plate of the stay is turned up at right angles to form a flange which 




Fig. 48. 



is then riveted to head and to shell. The stays do not come close to 
the corner of head and shell, so that in cutting away the heel of the 
right-angled triangle the fourth side may become parallel to the 
hypothenuse of the original triangle. The stays are usually placed 
radially upon the head. (See Figs. 98, 105, and 115.) 



64 



MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



Where a flat surface has no surface parallel to it to which it can be 
directly stayed, and the length is too short for wise use of diagonal 
bracing, the surface must be made stiff by bars acting by their stiffness 

Hke girders to prevent deformation 
or collapse. This is met in the 
flat crown sheets of locomotives and 
in combustion chambers of marine 
boilers. The problem is compli- 
cated by the intense heat upon such 
surfaces, which precludes the use of 
solid bars, which would keep water 
from the metal. 

The crown-bar method is shown 
in Figs. 112 and 114, in which the 
bars appear in pairs, running 
across the flat sheet from side 
to side of the furnace. The sheet 
is stayed to these bars by J-inch 
bolts which pass up through the 
plate and between the two bars 
of each pair. The joint between 
head and plate is rhade by a 
copper washer, and the washer 
under the nut serves to bind the 
bars together. A taper washer or 
distance piece keeps the bars from 
the plate, so as to cause water to 
touch as much plate as possible, and keep the plate flat when the bolts 
are tightened. The deflection of these bars is prevented by sling 
stays when they are long, or their own resistance to bending is depended 
on if they can be short. Figs. 51, 52, and 114 show other methods, 
used either where the crown sheet is arched to approach parallelism 
with the outer shell, or where the outer shell is made flat to become 
parallel with the flat crown sheet. The stay bolts have taper surfaces 
under their heads, which draw into tapering reamed holes in the sheet 
by the pressure of the steam, and copper washers under the head help 
to secure tightness. Fig. 52 is called the Belpaire fire box. (See also 
Fig. 115.) 

Staying should not be too rigid, and it is very objectionable to have 
a flexible and a rigidly stayed surface attached to each other. The 
motion of the flexible part either from heat expansion or by pressure 
produces a great strain or a concentration of the deformation at the 




Fig. 49. 



BOILER RIVETING 



65 



margin where these tendencies to move and to resist motion meet. 
Tests have shown that in locomotive fire boxes where the difference 
in temperature of the outside and inside plates may be considerable 



B 



Fig. 50. 

the expansion of the latter brings so serious a cross stress or flexure 
upon the rigidly held bolts as to exceed their elastic limit. Ultimately 
therefore by repeated stress these bolts fail close to the thread, and the 



-"■"•-1 1 



li^sm /j^' "^ 



rrrrn-H-i- 



il ill 



Fig. 51. 



plate bulges and leaks, or the plate cracks. To ehminate these diffi- 
culties and allow lateral motion while resisting deformation in the 
direction of greatest stress, forms of flexible socket connection have 
been devised of which one is shown in Fig. 53. The end of the bolt is 



66 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

spherical headed, fitting in a cup. This cup screws into the outer 
plate from without, and a cover cap makes all tight against leakage. 
The angle of the bolt can vary through more than the necessary range 





+ -T-+— ^--too' 
+ 4 + -f -t -••- 4 •+ -t -f ■(< -t O 1| 
+ + + +4-1- + + . + + -(--+-» +T" 
-t--*--l-+ + + 4-+ + + -t-t ++il 
h-t + + ++ + -*--i--r-f-t---f + -t-;| 
t4 -4-4--4--+++ -•-++ -^ + + -rii 
-+ +-+-+-+4--t -^ + ^■4-t++;l 
+ + + +H-+ + + + + +-4— t + +il 
+ 4- -♦ -I- -f + + +■■»--•--+ 4- + 4+|. 
+ -t-4.+ + -t+-t-+4 +t + + -ii; 
+ -V + + -<-4-4 + + -t-+-t-|-+,4ji 
4H.444-4.4 + 4-+4--V4 + +,] 
+•+ -^ -4- 4 4 t + -t- + 4 + 4 + ^1, 
-r + 4444-t + -)- 4 — H 4 4 4 -+11 
4 -f H- 4- 4- + 4- +- -+.+—♦--1- H- + +|l 




Fig. 52. 

without cramping the bolt. The other end screws into the inner plate 
and is headed over, and a simple flexure of a beam fastened at one 
end takes place instead of the complicated flexure and shearing which 
must appear when both ends are rigid. When 
motion is restrained at corners as at the joint of 
shell and head, or of a rectangular fire box the 
phenomena of grooving are apt to occur where 
the flexure of the plate is greatest. 

45. Manholes. In the construction of riveted 
shells a provision must be made to allow the 
helper to get out who has " held up " for' the 
final riveting of the last joint. Access must also 
be had to the inside of the boiler for inspection 
when in service and for repairs. The function of 
this hole is thus to let a man in and out, and 
is for this reason called the manhole. It should 
be as small as possible to effect its purpose, 
because the metal of the shell removed to make 
it is equivalent to just so much strength removed 
from the boiler. Measurements show that the 
average man is fourteen inches on the axis of 
the longest dimension through the articulations 
of the hip-joints with the pelvic bone. The 

shoulder dimension, though naturally larger, is flexible and con- 
tractile, and any man can pass through a hole through which his 
hips will pass. The dimension at right angles to the line through the 




BOILER RIVETING 67 

hip-joints is normally less than the other, and is a flexible one when 
it is not less. Hence the manhole receives an elliptical shape with 
its long axis 14, 15, or 16 inches long, and its short axis 9, 10, or 
11 inches, or four or five inches less than the other. This elhptical 
shape- has furthermore a very practical advantage, in that the lid 
which is to cover the hole and must have a size larger than the 
hole, so as to lap over the edges, can be made to fit upon the inside 
of the hole and can yet be itself passed through the hole from 
without. The lap over the edges must be less than one-half the 
difference between the long and short axes of the elliptical hole. If 
the hole must be circular, the lid has to be external. 

The Hd is held to its seat over the manhole when internal partly 
and mainly by the pressure upon its inner side; but to make the joint 
steam-tight, and to hold it from displacement at other times, the lid 
has one or two studs symmetrical upon its long axis, which pass up 




Fig. 54. 

through a proper hole or holes in a bridge or *' dog " of cast or wrought 
iron which spans the manhole opening, so that when the nut is screwed 
down upon the stud and bears on the outer surface of the dog, the lid 
is drawn to its place and held firmly by the nip of the dog upon the 
edges of the hole (Fig. 57). The joint between the hd and the plate 
is made tight by a gasket of rubber or asbestos board or similar mate- 
rial whose compressibility shall compensate any inaccuracy of contact 
surfaces. It is rare that finish of surfaces can be secured or maintained 
which will make a true metal-and-metal joint without gasket under the 
conditions prevailing around a manhole. The hole cut in the plate of 



68 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

the boiler leaves the strength less than when the metal was solid, at 
the zone whose width is the span of the hole. All the circumferential 
strains in the ring of plate are transferred around it till at the edge of 
the hole they are balanced by no counteracting force except that sup- 
plied by the reluctance of the material to spHt into filaments by yield- 
ing sidewise. The tendency can be illustrated by a band of elastic 
material like rubber with a hole punched in it. Under strain length- 
wise the hole becomes deformed, and most so at the ends or at the 




Fig. 55. 

points farthest from the solid material at the sides of the hole. Hence 
it is desirable not only to place the hole, if in the shell, with its short 
axis lengthwise, but also to reenforce the weakened plate around the 
edge of the hole; and this practice has given rise to manhole mouth- 
pieces or nozzles. The simplest form is a forged ring of wrought iron 
(more desirable than a similar ring of cast iron) riveted around the 
edge of the hole in the plate. The lower surface will be plane to form 
the flat seating for the cover, while the upper surface conforms to the 
shape of the boiler. The rivets are in countersunk holes on the face of 



Fig. 56. 

the seating, or else the ring is broad enough to allow the line of rivet- 
heads to come beyond the lap of the cover. Such ring resists the tend- 
ency to flex which will occur when the manhole is upon a cylindrical 
surface and metal has been cut away which would maintain the shape 
when the pressure came upon the continuous ring of plate. Fig. 55 
shows the ring made of a flanged plate riveted within the shell, and 
Fig. 56 the exterior nozzle arrangement. The interior seating offers 
some advantages from the resistance to flexure which it gives. Fig. 57 
shows a full detail of the manhole with seating and hd of cast iron, 
and Fig. 58 the more approved steel seating and lid. For greater 
security in large holes the dog and bolt may be doubled, one on each 
side of the short diameter. 



BOILER RIVETING 



69 



The location of the manhole will be either upon one of the heads, 
or upon the head of the dome of the boiler, or upon the shell, or upon 
that attachment called the mud drum. On the cylindrical or spheroidal 




Fig. 57, 




Fig. 58. 



surfaces of shell or dome or drum, seatings or nozzles are a necessity, 
to secure planes for the covers to seat themselves upon; on flat surfaces 



70 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



they are desirable for strength and stiffness. The construction of the 
boiler may require more than one manhole, a condition frequent in 
marine practice. 

46. Hand-holes, as their name indicates, are smaller openings in the 
shell to give access to the hand for an inspection by touch, or for 
convenient cleansing or minor repair. The construction is the same 
as for the manholes, the reenforce or 
seating being of boiler plate or a flat ring 
of wrought iron. Their location and 
number will be determined by the 
design of the boiler in order to serve 
their purpose and leave no corner which 
inspection cannot reach. Fig, 59 shows a 
typical hand-hole structure. 

47. Edge Planing and Calking. The 
shearing of the steel plates to size has 
left an edge or selvage of metal which is 
brittle and unreliable from the effect of 
the shearing plates. This deteriorated 
metal should be planed away by a 
cutting tool. Fig. 60 shows such an edge 
planer for plate, the sheet being held by 
the clamping screws as in a vise, while the 
tool traverses along the edge. It is con- 
venient to give the edge a bevel in 
planing, which is not only of service for 

appearance' sake, but gives an edge at the lap or joint to be used 
in calking the seam. 

It is too costly to finish the flat surfaces of the plates where they 
lap so as to make a joint which would be steam- or water-tight under 
the compression of the contact areas by the rivets. There is always 
som.e scale or roughness from the hot rolling process and the later 
bending and flanging. Hence the seams must be calked, from within 
or from without. It is usually easier to do it from without and the 
process is that of upsetting the lower edge of the bevelled sheet into 
the joint by means of a round-nosed chisel held against the edge 
and struck with a hammer. Fig. 61 shows the method of calking with 
a round-nosed tool, which is much to be preferred to the sharp-nosed 
chisel, although the latter is easier to use. The sharp corner of the 
sharp tool may indent the lower plate at the joint, and thus start 
the first crack whose ultimate consequence will be the weakening of 
the plate at that point, which the illustration suggests. 




Fig. 59. 



BOILER RIVETING 



71 



'M 




72 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

48. Disengagement Area. Water Space and Steam Space. Following 
the analogy of the tea-kettle as the prototype of the modern boiler in 
cylindrical form, how full of water is it desirable to keep it when at 
work making steam? The more water it holds the more heat stored and 
the less the fluctuation of pressure range. If too full of water, the 
free surface of contact of boihng water and steam gas grows less and 
less, and the volume of stored steam is less, with attendant tendency 
to fluctuation of pressure. This surface will be a maximum in the 
cylinder when the water stands at the level of the horizontal diameter. 
To put it lower than this makes it difficult to prevent overheating of 
the shell, because the hot gases are likely to come in contact with 
elements of the cy Under which are not water cooled. Hence the 
water will normally be at a higher level than this. How much can the 
free surface be safely diminished by carrying the water higher than this? 

If too much steam must escape from too small an area, the rising 
steam gas keeps the surface of the water bubbhng and frothing. The 
steam hfts the top layers of water, so as to give a fictitious indication 
of level of water, and entrains with it a proportion of water in drops 
or mist or even in some mass in its too rapid flow from the surface of 
the water to the outlet pipe. Such foaming or frothing occurs when the 
boiler is hard pushed and there is oil or floating scum on an alkaline water. 
When the foam becomes solid water, and such water passes over into 
the steam pipe, the boiler is said to " prime." The presence of a scum 
of dirt or of grease increases the tendency to foam and prime, because 
the steam gas forces its way out by bursting through this scum, but 
to carry the water level too high is not only to bring the disengagement 
surface nearer to the pipe outlet for steam, but it is also to diminish 
its area. A boiler forced to evaporate faster and disengage more steam 
than at its normal rate will also be likely to foam and prime. 

The accepted standard for early practice was to make the volume 
filled with water (called the water space) to be two-thirds of the volume 
of the boiler, while the space in which steam is confined above the 
water (called the steam space) should be the remaining one-third. 
This was reached by making the area of the head to be divided by the 
water line into segments whose area was as 2 is to 1. 

This was an empirically correct ratio, based on observation, but lacked 
a rational basis, because the real store of steam is not in the steam 
space, but in the heated water. A more satisfactory basis is the 
disengagement area basis, and experiment has shown that when the 
flow of steam from the water into the steam space is at a rate such that 
it would fill the steam space three times a minute, the disengagement 
was slow enough to give no trouble from priming. This experiment 



BOILER RIVETING 73 

was made on a marine boiler, and trouble was found from entrained 
water when the evaporation had to be so rapid that the steam space 
was filled five times per minute; at four times per minute trouble was 
occasional but not continuous. Stated otherwise, a linear velocity of 
flow of steam faster than 2 feet per second through the water surface 
will entrain water with the steam. The larger the cylinder volume 
to be filled per stroke, or the greater the number of strokes per minute, 
or the greater the volume of steam required per minute, the larger the 
aggregate steam space required if pressure is not to be allowed to 
fluctuate when the disengagement rate is normal and slow enough 
to prevent priming. 

49. Domes and Steam Drums. The difficulties in the engine cylinder 
from entrained water will be hereafter referred to (paragraf 259), and 
are so serious and important that special pains must be taken to prevent 
priming or foaming as a continuous process. This is done by so reducing 
the rate of flow of steam at its intended entry into the steam pipe that 
time and opportunity shall be given for water entrained by the outrush 
of steam from the disengagement area to settle back within the boiler 
by gravity before such water acquires the greater velocity in the pipe 
itself. An enlargement in the cross section of the pipe will permit 
such lowered exit velocity and tliis is secured by the dome or steam 
drum. The dome which appears on most massive or shell boilers is 
an upright cylinder of boiler plate of some considerable diameter, up 
to two-thirds that of the shell and so attached to it as to form part of 
the steam space or an addition to it. In horizontal boilers it will have 
its axis at right angles to that of the boiler, and will be attached to it by 
flanging the sides of the dome outward, and curving the sides so as to fit 
the curvature of the top of the shell (Fig. 65). The shell is cut away 
under the dome in the type form to the full diameter of the dome. The 
steam outlet will be a pipe passing from the top of the dome or near it. 

It will be apparent that the dome accomplishes three purposes: 

(1) It removes the inlet to the steam pipe farther from the disengage- 
ment area than it could be if it were on the shell directly; water is less 
likely to spatter or be projected into the steam outlet. 

(2) The linear velocity of steam is low in the large cross section of the 
dome. Entrained water is less likely to be carried at low linear velocities 
than high, and it has time to separate out from the steam by its greater 
specific gravity. 

(3) The steam flows to the dome from a larger proportion of the dis-- 
engagement area than it would to a small neck or nozzle on the shell. 
Under a neck or nozzle the water is heaped up (Fig. 5), and the greatest 
disengagement occurs at that point, a condition favorable to priming. 



74 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

The dome is usually put at that point on the length of a boiler at which 
experience shows the disengagement to be most active, so as to avail of 
this action, and to prevent injury caused by a disregard of the tendency 
there. 

The objections to the dome are the weakening of the shell from the cut- 
ting away of the metal under the dome, whereby not only is the strength 
affected, but the cylindrical shell tends to flatten under the pres- 
sure, and this results in leakage at the dome seam at the top. The 
shell is an unstiffened curved stay where the hole is cut, and the double 
thickness of the lap of the dome joint does not replace the strength of 
the unbroken cylindrical surface. Hence the dome joint is further 




Fig. 65. 

stiffened, either by turning up the plate into a vertical flange, or by a 
stiffening ring, as was described in manhole seatings (paragraf 45). 
Fig. 66 illustrates these methods. 

This objection to the weakening of the shell by the hole for the dome 
has induced designers to seek to secure the functions of the dome without 
such cutting of the shell. 

(1) The shell has been perforated with either many small holes or one 
larger one under the dome, but not cut away entirely (Figs. 67 and 68). 
The area of the holes should aggregate several times greater than the 
area of the pipe. The objection to this is that the tendency to straighten 
is not removed, because the pressure in the dome balances the pressure 
below the perforated surface, and there is no tendency to keep the 



BOILER RIVETING 



75 



cylindrical shape. The plate acts Hke a curved stay only. Moreover, 
the dome cannot be used as a means of entry to the boiler, unless the 
hole in the shell is the full size of a manhole, and the top of the dome 
is a convenient place to enter and to place the manhole. 

(2) To attach the dome by a neck (Figs. 69 and 72). The flanges 
of the neck return some strength and stiffness to the shell. It is more 
convenient, if this is to be done, to make the dome a horizontal drum 
(Fig. 73). 

(3) To use a horizontal drum or pipe of large diameter overhead, to 
which the boiler will be connected by a neck if but one boiler is used. 
This plan is specially convenient where several boilers are side by side 




Fig. 66. 



or in a " battery," as it is called. All can dehver into a common drum, 
and from this a drainage connection may remove any entrained water 
which may be carried through neck or nozzle by high velocity of steam 
currents. Figs. 69 and 73 will illustrate this arrangement when the 
drum is transverse, and is really a large pipe merely jointed to each 
boiler by piping which allows of expansion without cross strain. (See 
also Figs. 137, 148 and 189.) 

(4) The use of a dry pipe with perforations. Figs. 71, 98, 106, 122 
and 123 will show this arrangement. The steam leaves the disengage- 
ment surface to pass into the steam pipe through a number of small, 
holes in the interior pipe which is a prolongation of the steam pipe 
inside the boiler. The gentle current into each opening prevents 
entrainment of water, because the aggregate area of openings is in 



76 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




Fig. 67. 




Fig. 68. 



BOILER RIVETING 



77 



excess of the area of the pipe. The objection is the stoppage of the 
inlet holes in muddy waters. This is an arrangement' used in marine 
practice and in some locomotives and is favored more and more in high- 
pressure land practice. The weight of the dome is an objection on 
board ship, and an elevation of the center of gravity of the boiler, and 
on some locomotives the dome has been objected to because, in addition 
to its other drawbacks, it stands in the way of the view of the engine- 
man. Where the locomotive boiler has a dome the throttle box will be 
near its top, and the pipe to the cylinders runs down through the steam- 




space. With a perforated dry pipe the throttle box will be at that end 
of it at which it comes out through the front head of the boiler. The 
arrangement of Fig. 72, while known as a '' mesh separator," is in effect 
the same as a perforated dry pipe, but is removable for cleaning or 
repair. 

(5) A form of separate dome has been used for marine boilers on 
smooth waters in which the dome is an annular cyhnder and has the 
smokestack-flue pass up through it. This has prevailed in river-boat 
practice, and was particularly convenient in wooden hulls, because the 



78 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




BOILER RIVETING 



79 



" steam chimney," as such dome was called, could get no hotter on its 
outside than the heat of the steam. The dome was high, and the effect 
of the hot chimney gases within it was to dry or even to superheat the 
steam in the annular space (Fig. 101). 

Dome heads are rarely made of cast iron and only for moderate and 




Fig. 71. 

low pressures. The greater thickness of metal required with cast iron 
is convenient for attaching manhole fixtures, valves, and pipe outlets, 
and the dome head is not exposed directly to heat nor to sudden 
changes of temperature. The unreliability of cast iron (paragraf 37), 
is still against it even here. Flanged wrought iron or steel is better and 




Fig. 72. 



will be generally used, and will be universal for high pressures and 
large diameters, especially where staying must be done (Fig. 68). 

50. Mud-Drums. It will be noted in detail hereafter that many 
boiler-feed waters are impure and contain or deposit mineral matter 
which remains in the boiler after the water is evaporated (paragraf 
185). It is convenient to gather such soHd material under the gen- 



80 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

eral name of " mud " in a special part or element of the boiler, and 
keep it if possible from settling upon parts of the heating-surface where 
its presence would do more harm. Hence the mud-drum will be an 
inverted dome or a drum at the bottom or coolest part of the boiler, 
and connected with it by a neck- or nozzle in line with those currents 
of circulation within the boiler which will direct descending solid matter 




Fig. 73. 



into the drum, with the view that, when once within the drum, the 
absence of circulation therein would prevent any mud or like material 
from coming out again (Fig. 73). The mud-drum is therefore with- 
drawn from contact with hot gases by encasing it in brick, or by having 
it where the gases only meet it when cooled by contact with other 
parts of the boiler. Fig. 74 shows the mud-drum B with an axis 
parallel to that of the boiler. It is more often transverse to the boiler. 
It usually has a manhole-opening when large, or when much trouble 
is expected from hard scale from the water. In small sizes a hand- 
hole will be enough. From it the blow-off pipe is led off so that mud 
can be blown out by opening the valve with pressure within the boiler. 
The feed-pipe delivering fresh water to the boiler sometimes enters 
the mud-drum, but this is not the best place. (Fig. 73.) 

The mud-drum in pure waters often reduces to a very small append- 
age or disappears entirely. The difficulty with it occurs when care 
has not been taken to guard against its expanding at a different rate 
from that of the boiler itself, because cooler, while rigidly attached to 
the latter and not free to move. This brings strain at the connecting 
neck or necks, followed ultimately by leakage and by corrosion at 
those points. 

51. Concluding Comment. Classification of Types. In the fore- 
going paragraphs of this chapter, the purpose has been to discuss the 
structural detail of all boilers belonging to the steam-kettle or shell 
type in which steam is made by fire under a pressure-resisting vessel 



BOILER RIVETING 



81 




82 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

of considerable volume. While the illustrations include also other 
details as of the furnace, support, and operating accessories, these are 
apart from the primary purpose. The next step must be a differenti- 
ating of types and study of the derivatives of form from the simple 
fundamental conception heretofore before the mind. 

The demand for increased power has continually called for the liber- 
ation of more heat in the furnace per unit of time, and the more 
effective transfer of that heat to the water and steam. With more 
rapid combustion rate (paragraf 12) the fire temperature increased, and 
therefore the extent and amount of heating surface to absorb it, and 
prevent the hot gases from leaving the boiler at too high a tempera- 
ture. The one object sought has been to bring every particle of water 
to be heated and evaporated into close and effective contact with 
every particle of gas which was hotter than such water; and in general 
the method to do this must be to break up water and hot gas into 
small volumes and thin films or elements of small thickness between 
their two nearest sides to secure such rapid and complete transfer of 
heat. This fundamental purpose has been sought along the two pos- 
sible lines. The first is to subdivide the volume of the hot gases and 
cause these to pass in small streams through the water whose mass 
w^as thus subdivided. This may be called the '' fire-tube " idea, em- 
bodied in tubular and flue boilers, and reaching its limit of principle 
when the fire itself is placed within the mass of water to be heated. 
The second line is the keeping of the fire undivided, but so subdividing 
the water volume by the use of many smaller cyhnders or tubes as to 
secure the intimacy of contact with fire and hot gases. This may be 
called the " water-tube " idea, in that the water is within the pres- 
sure unit as in the kettle, and the fire is outside. In the other or 
fire-tube idea the water is outside and the fire is within. In fire-tube 
designs the tubes or cylinders are exposed to collapse from pressure 
directed radially towards their center: in water tubes the pressure 
tends to burst them radially outward. The sectional boilers are all 
in the water-tube class, as are the coil and flash types. 

It would have been convenient if the distinction of terms ''exter- 
nally-fired " and " internally-fired " could have been used as essentially 
synonymous with the water-tube principle and the fire-tube principle 
respectively. But while all water-tube types are externally fired in 
both senses, some fire-tube types also have the fire external to the 
water, and are therefore properl}^ called externally fired. In the 
following the fire-tube principle will be first treated, external and 
internal, because historically these were first. The water-tube or sec- 
tional principle is the important modern development and is specially 



BOILER RIVETING 



83 



well adapted for use with the higher modern pressure both ashore 
and afloat. The classification of type will therefore be: 



Fire-tube 



Water-tube 



Externallj'^-fired 

Internally fired 

Combinations 

Plain cylinder 

French Elephant or Union 

Sectional 

Coil or pipe 

Flash and semiflash 

Combinations 



i Tubular 

!Flue 

[Cornish and Lancashire 

I Locomotive 

[Marine 

i Upright and fire engine 



It is obvious that the two principles of subdividing the heating and 
cooHng masses may be combined in one design, adding water tubes 
to a boiler whose basal classification is in a fire-tube class. These, 
however, can be covered in both groups under the general designation 
of combinations. 



, 



CHAPTER IV. 

FIRE-TUBE BOILERS EXTERNALLY FIRED. 

55. Types of Boiler in the Fire-tube Class. In the externally fired 
fire-tube class are those in which a cylindrical shell is used to contain 
the water and resist the pressure, and the grate and fire are under this 
shell, usually at one end. (Figs. 75 and 76.) 

The depth of the grate may be enough to burn the desired weight of 
coal per hour, provided it is not so deep as to exceed the limit of easy use 
of the firing tools. The fire on the grate imparts its heat by radiation 
from its solids to the part of the shell over it, and the flame passing 
backward radiates its heat as long as the flaming process continues. 
After the flame ceases the hot gases lick the bottom of the shell until the 
back of the boiler is reached; here they pass by subdivision either into 
a small number of large diameter flues, or into a large number of small 
diameter tubes. The latter is the type of its class and is called the 
tubular or multitubular boiler. The other is the flue boiler. These 
tubes or flues pass through the water-space of the boiler (paragraf 48), 
and by breaking up the volume of gas into thinner bulk cause the cooling 
effect of the water or heating effect of the gas to be more effective. 
The cooled gases leave the shell at the front head and join into one 
stream again in the smoke-box. 

56. The Tubular or Multitubular Boiler. Fig. 76 shows a cross- 
sectional elevation of a multitubular boiler. From Figs. 75 and 76 it is 
apparent that for a boiler of D feet in diameter and L feet long and 
having n tubes of d inches external diameter the water contact for 
absorbing heat or the heating surface in square feet will be 

TzDL jcdLn 
Heating surface = — ^ — ■ -\ — -• 

As n is a large number, such a boiler has a large heating-surface, and is, 
therefore, effective in steam-making and in cooling the gases. It is a 
question whether the lower elements of the tubes are as effective as the 
upper ones, since the former become quickly coated with dust (Fig. 8) , — 
a non-conductor of heat, — and if any liquation or separation by 
specific gravity takes place in the tube, the hot gas is at the top and 
the cooler at the bottom. The bottom elements on the water side are 

84 



FIRE-TUBE BOILERS EXTERNALLY FIRED 



85 




86 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

not good steam-makers either. Some designers compute only the 
upper half cylinder of the tubes as heating-surface, or introduce a 
factor 2 in the denominator of the last term. (See Fig. 8.) 

An empirical rule of proportion for the chimney area in terms of the 
grate surface which has seemed to work well has been to make the 
chimney area one-eighth of the grate area. As the gases are hotter 








Fig. 76. 



before entering the tubes or flues, it is best to make the aggregate cross- 
section of the open or internal diameter of such tubes to be one-sixth 
or one-seventh of the grate area for flaming or gaseous fuels. With 
anthracite it can be reduced to one-tenth so far as easy passage of the 
gases is a factor at not too high velocity. This tube area was formerly 
called the calorimeter of the boiler — a most unfortunate term at any 
time, and now no longer in use. 

Another empirical rule of practice is to make the tube diameter bear 
to its length the ratio of one-inch diameter to four feet of length in 
bituminous or flaming-coal practice, and to five feet of length with 
anthracite. The table in the next paragraph gives some further data. 



FIRE-TUBE BOILERS. EXTERNALLY-FIRED 87 

In common practice the top row of tubes is from four to six inches below 
the normal water line; five inches is usual. 

57. The Tubes for Fire-tubular Boilers. The tubes for boilers are of 
a special grade of stock, and are designated by their external diameter, 
and not by their opening or internal diameter as in the case of pipe. 
The plate to be used in making the tubes should be either of steel or of 
charcoal iron. The joint is to be lap-welded, and most carefully and 
completely done and tested. Drawn tubes of steel have been used 
in a few costly boilers, so as to avoid the possible defect of the weld. 
Copper and brass tubes are used in a few special boilers, such as small 
motor-vehicle and fire-engine practice where great conductivity for 
heat is demanded, but always in small diameters only. 

The hole for the tube in the heads or tube-sheets is made just large 
enough to take the tube. In thin plate, and for small tubes, these holes 
may be punched by a spiral punch 
(paragraf 32, Fig. 20), but a ^^^T^ 



drilled hole is better, beveled or 

chamfered to give additional hold ^ ' \ ^ 

for the tube. Or it may be specified >r / 

that the hole be rounded on each 

side with a radius of yV of an inch 

so as not to cut into the tube. Q ^CIL I _ 

Fig. 77 shows the usual type of 

''pin" or 'Hit" drill used for larger Fig. 77. 

holes, a small hole being first 

punched or drilled, and then the remaining metal being cut away 

like a washer, without reducing all the material removed to chips. 

The cutter may be made adjustable. Special reamers then finish the 

hole. 

The tube is then secured in the hole by the process called " expand- 
ing." A tube-expander (Figs. 78 and 79) may be of the roller type or 
of the sectional type. 

In the roller form three rollers are borne upon segments which guide 
them, and upon which radial pressure can be brought by the central 
conical or tapering pin. When the rollers inside the tube are opposite 
the tube-sheet or just behind it, upon the inside of the tube, the rollers 
are forced outward and revolved inside the tube. The rolling pressure 
causes the metal of the tube to flow outward until the resistance of the 
hole in the tube-sheet is encountered. Then the tube and the hole are' 
pressed to fit each other (Fig. 81), with a force usually sufficient to be 
steam-tight and having a very considerable strength. To prevent the 
tube and its sheet from sliding under changes of length due to tem- 



88 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

perature, the end of the tube is sUghtly turned over or upset — called 
beading — so as to grip the outer face of the tube-sheet. This both 




Fig. 78. 




Fig. 79. 



Fig. 80. 



adds to strength and serves to prevent leakage. The beading is usually 

done with a special form of swaging-chisel (Fig. 80), often called a 

^' thumb-swage " from the shape of its 

pressure end, which has a longer prong 

which enters the tube, while the shorter 

prong projects over the annular tube end, 

and gives an aspect suggesting the combination of index-finger and 

thumb on the human hand.' 

There are other forms of tube-expander, acting by wedging or direct 
pressure, but the roller form takes less power and gives better results. 
The fit of the expanded tube is a pressure and frictional one. Hence 
any tendency to push or pull the tubes through the tube-sheet (from 
heat or from yielding to pressure) causes the expanded tubes to leak 
in their holes. With high pressures a certain proportion of the tubes — 



ii 



FIRE-TUBE BOILERS EXTERNALLY FIRED 



89 



one in five, often — are made of extra-heavy stock, so as to allow for 
a greater strength due to the more efficient heading or beading of the 
thicker metal. Or, again, with thicker stock in the stay-tubes, the 
outside which projects beyond the sheets can have a thread cut on 




Fig. 81 



it, upon which a stay or lock-nut will be screwed home, and thus con- 
vert the tube into a through-stay. Such stay-tubes will be located 
where the tendency of the heads to flex under the pressure needs partic- 
ularly to be guarded against. 

Expanded tubes can be re-expanded so as to be made tight if leak- 
age should be developed by service; but this cannot be done very often, 
since the metal must undergo a pressure in expanding which tran- 
scends the elastic limit of the material (otherwise it would spring back 
when the expander was withdrawn), and as the result the tube is apt 
to crack when the process is overdone. The leakage occurs when the 
tubes become overheated from any cause which prevents the water 
from effectively coohng them. In such overheating they expand, and 
in the effort to lengthen they force themselves through the holes in 
the tube-sheets opening the joint, which does not re-form itself on sub- 
sequent contraction. Upright boilers of certain type are specially 
prone to this. 

The cutting off of the tubes to length is done after the tube is in 
place, either with a special gauged cutter revolved by hand or power, 
or in simpler practice by putting a gauge-plate of hard steel against the 
tube-sheet over the tube and cutting down to it by hand. The thick- 
ness of the gauge gives just the amount for heading and beading. 

After tubes have leaked and cracked and re-expanding is impossible, 



90 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

or when a tube has failed from any cause in its length, it can be removed 
by cutting out. The same tool can be used for cutting tubes inside 
the heads as is used for cutting off outside (Fig. 82). The defective 




Feed Stop 



Fig. 82. 



tube can then be replaced as in the first instance with a new tube, or 
new ends can be welded on such as are defective at the ends only, using 
the good stock of the old tube. The commercial length of boiler-tubes, 
in 12, 16, or 20-foot lengths, usually fixes the length of the boiler itself . 
See Table YII. 

58. Ribbed Tubes. Retarders. A special form of boiler-tube has 
been used to some extent, which is fitted with ribs lengthwise, or is 
thickened at several points of its inner circumference (Fig. 83). The 
object of this is to arrest more completely the 
available heat in the hot gases flowing through 
the tube, so that from this extra metal the heat 
may be abstracted by conduction. A somewhat 
similar function is discharged by what have been 
called retarders in the tubes. A cross-shaped bar 
the length of the tube is laid within the ordinary 
cylindrical tube, and absorbs heat from the gases, 
which it transfers to the tube by radiating such absorbed heat, as 
well as acting to retard the too-rapid flow of gas at such a rate as 
would prevent complete transfer of heat to the tube. Such retarder 
may be twisted into a helix to hold the gas longer in the tube. 

An objection to the ribbed tube is the difficulty in cleansing it when 
the gases deposit a sticky residue on the cooler surface of the metal. 
The retarders are cleansed by being taken out. 

59. Arrangement of Fire-Tubes. While the purpose for which fire- 
tubes are used is best served by a large number of them, yet this may 




Fig. 83. 



FIRE-TUBE BOILERS EXTERNALLY FIRED 



91 



be carried so far as to sacrifice some other good features. In the first 
place the nest of tubes should not come too near the external shell. 
Space should be left to permit a descending circulation of water out- 
side the tubes (Fig. 5), and to permit inspection and cleansing of the 
plate from above or below, or both. Three inches in small boilers and 
four to six inches in larger ones is the recommended space. 

It is a good plan to leave out a vertical row of tubes in the center 
of the nest; or, if this number cannot be sacrificed, to make the clear 
horizontal space between tubes two inches in the center and one inch 
elsewhere. When the fire is forced, steam generation will be most 
active in the part nearest the fire, and the current of gas will rise in 
the center, lifting the water here higher than at the sides, and stimulat- 
ing the descent at both sides. Through this opening also cleansing 
of the central elements and rows of tubes can be more easily done by 
a tool which will reach down. 

If there is a manhole for cleansing in the front or back head below 
the nest of tubes to give access to the lower elements of the shell 
(Fig. 54), this will compel the omission of some tubes at the bottom 
of the nest. Such space at the rear of the boiler becomes a sort of 
mud-drum for the accumulation of solid matter, and it should be easily 
cleansed. These together lead to arranging the tubes in two nests, 
sj^mmetrical respecting a vertical plane through the axis. 

The tubes will be arranged in horizontal rows. It is best to place 
them also in vertical rows or under each other in a horizontal boiler, 
rather than to " stagger " them by placing the tubes in alternate 
rows vertically under the spaces between tubes on the row above. 
The latter gets more tubes in; but circulation is not so easy, and 
cleansing of rows below the upper two becomes impossible if mechanical 
scraping is necessary. Tubes may be staggered in upright boilers, 
as scale does not settle on vertical surfaces; but cleansing of the lower 
tube-sheet becomes then impossible toward the center. In vertical 
rows with space between reasonable cleansing by scraping can be done 
from above. Table VII gives facts and standards of arrangement. 

TABLE VII. FIRE-TUBE PROPORTIONS AND ARRANGEMENT. 



Diameter of 
Shell in 
Inches. 


Tube 
Diam. 
Inches. 


Usual Num- 
ber. 


Vertical 
Cto C 
Inches. 


Horizontal 
Cto C 
Inches. 


Length Over 
All. Feet. 


Center of Up- 
per Row of 
Tubes Above 
Center of 
Boiler. 


48 to 60 
48 to 66 
54 to 72 


3 

H 
4 


46 to 76 
34 to 70 
36 to 74 


4 
5 


4i to U 

5 to 5i 

6 


10 to 12 
12 to 16 
16 to 20 


6i to 8i 
6ito 9i 
7 to lOi 



92 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

The tubes of a tubular boiler not only take off area from the head 
exposed to pressure, but they also serve to stay the two opposing 
heads together. It is only necessary therefore to stay the segment of 
the flat head above the top row (see paragraf 44). The head is always 
flat for convenience of the expanding process, and the radius of the 
curve of the flange which is formed on it to fasten it to the shell is often 
specified to be not less than a minimum — usually H inches. A 
larger radius even up to four inches will cause less strain to the extreme 
fiber in flanging. 

60. The Flue-Boiler. When the fuel burned on the grate is of such a 
bituminous or gaseous type that its flame exceeds in length the over- 
all length of the shell, the tubular boiler becomes uneconomical because 
the fine subdivision of the still glowing flame makes it go out in the 
cooler tubes. No more oxygen can reach the flaming gas to support 
combustion, and combustion in progress ceases because the temperature 
of the gas in the small tube falls quickly below the point of sustained 
ignition. The glowing flame becomes a smoke, and carbon goes off 
with the gas in an unburned state as CO or as lampblack or soot, which 
might have given heat to the water. A larger tube is required. 

When the water contains much solid precipitable matter which will 
form a scale on the heating-surfaces which is hard to get off, the fine 
subdivision of the water around the small tubes of the preceding type 
offers many surfaces which are hard to reach for cleaning by mechanical 
abrasion. Hence a type of fire-tube boiler is suggested where there 
will be larger fire-passages and larger water-masses. If the tubes are 
larger, there must be fewer of them in a boiler of a given diameter of 
shell. Such tubes, when of 7 inches external diameter or over, are 
called flues, and the boiler using them is a flue-boiler (Fig. 84). The 
formula for heating-surface of paragraf 55 applies here also, as the 
setting is the same but as the value of n is smaller, the heating-sur- 
face for a given shell diameter and L is less. It may be convenient, 
therefore, to increase the length. 

The greater diameter of the flues permits a joint with the head or 
tube-sheet to be made by flanging the holes in the latter and riveting 
the flue to the flange. These flanges may be internal (Fig. 85), or 
external (Fig. 84). Internal flanges should always be used where the 
ends of the flues are exposed to flame, as at the back end of the setting, 
since the ends of the tubes and flanges are cooled by conduction only, 
and not by contact with the water. External flanges are easier to rivet 
and are safe for the front or cooler end of the shell, and have to be used 
with small-diameter flues in any case. The number of such flues will be 
as great as possible when regard is paid to the limitations which they 



FIRE-TUBE BOILERS EXTERNALLY FIRED 



93 




94 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




FIRE-TUBE BOILERS EXTERNALLY FIRED 



95 



are to help to meet; two of large size being the lower limit (Fig. 85). 
They may be of tube up to the limit of its size of manufacture (usually 
18 inches); above that of riveted boiler steel with butt or lap-joints. 
61. Reinforced Flues for Long Boilers. When the boiler and the 



X''^ 




Fig. 




flues become too long for the flue to be in one piece, it must be jointed 
either as the shell is, or by the bump-joint of Fig. 86 where one segment 
is locally enlarged at the end for a short distance and the other piece 




Fig. 87. 



telescoped into it. With very large or long flues where they are exposed 
to stress and consequent deformation by their own weight, the flue must 
be kept to its cylindrical shape to give it strength against collapse, and 



96 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

this is best attained by means of rings of stiff section placed around the 
outside of the tube and riveted to it, or by the corrugated flue to be 
hereafter discussed (paragraf 68). Such stiff ening-rings may be of steel 
of angle or tee-iron section (Figs. 87, 88), with distance pieces to give 




Fig. 88. 



Fig. 89. 



free access of water to the flue-metal ; or the end of each flue segment 
may be flanged outwardly to make a joint with a flat ring placed 
edgewise between them (Fig. 89). They are corrugated ringwise with 
the same object. These stiffening-rings are either plain rings with 
light pressures, or else the ring receives a greater transverse resistance 
by being made of angle or tee-iron (Figs. 87 and 88). Or, again, the 
formation of the flue in several segments may be utiHzed as oppor- 
tunity to form up the joints into rings of stiffening effect, as in the 
Bowling and Adamson flue-joints of Figs. 89 and 90. 

The latter gives a longitudinal flexibihty to the flue which diminishes 
the strain on rivets in joints and at the heads when the flue gets over- 
heated or is suddenly contracted 
while the shell temperature re- 
mains constant. Illustrations of 
reinforced flues will appear in the 
next chapter, where the larger dia- 
meters are mainly in evidence. 

63. Conditions Suggesting Choice 
of Tubular or Flue Types. The 
distinction between the tube and 
flue is purely arbitrary. Under six 
inches is a tube, over seven inches 

is a flue. The tubular form is the type form for anthracite fuel and 
with good feed-water clean and free from mineral matter. It may 
almost be called the New England or Northern Atlantic Sea-Coast 
Standard, except where the sectional types come in. It is the form 




Fig. 90. 



FIRE-TUBE BOILERS EXTERNALLY FIRED 97 

before the mind of most every one not skilled in separating the types 
from one another when he speaks of '' a boiler." Its advantages are: 

(1) Great heating-surface in a small space. 

(2) This gives it ability to make steam rapidly, and to supply a 
great , deal of steam from a given area of ground occupied, as com- 
pared with certain other forms. 

(3) This evaporative capacity is cheaply bought. The tubular 
boiler is not an expensive one, but is the cheapest of the efficient types, 
costing under ordinary commercial conditions from $8 to $11 per horse- 
power. It can be made anywhere and by any boiler shop, with the 
usual equipment of tools. 

(4) The water is subdivided by the tubes into small masses, securing 
immediate transfer of the heat of the metal of the tubes to all parts of 
the volume of water. Hence the boiler responds promptly to an 
attempt to force it. 

As objections to the tubular boiler may be advanced: 

(5) The water-space is so filled with tubes that access to the lower 
parts for cleansing is difficult, and to some places is impossible. This 
objection is a fatal one if water is to be fed to the boiler which has great 
amounts of salts in it which are precipitated on boiUng. 

(6) The fine division of the gas-currents in the small tubes will so 
lower their temperature that they are extinguished. If the flame 
would naturally be longer than the length from the furnace to the entry 
to the tubes, the extinction of the incandescent particles on lowering 
the temperature makes the gases smoky, and carbon is wasted as soot. 
The fine subdivision in tubes is also fatal to further union of carbon with 
oxygen, and combustion, if not completed before the gases enter the 
tubes, will either be incomplete, or else will take place beyond the boiler 
at some possibly inconvenient place — such as the top of the stack or at 
its throat. 

The objections to the tubular boiler are the advantages of the flue 
type. With flaming coals and where the water is not good, it avoids 
some of the obstacles to the use of the multitubular. As the water 
becomes worse, the number of flues should diminish so as to give com- 
plete access for cleansing. As the fuel becomes gaseous and its flame 
lengthens, the flue should become larger in diameter. 

The tubular or small flue will be used wherever possible. 

U. S. FORMULA FOR FLUES. 

63. The U. S. Federal laws fix the formulae which are to be used in proportioning 
flues against collapse. They may be grouped as follows: 

Case A. For lap-welded flues greater than 1" in diameter and less than 16", 
and 18' long or less. 



98 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



P = ^ X 44. 

For each 3' of length add j^o o^ an inch to t. One wrought-iron stiffening- ring to be 
used in each 5', whose t' = t, and whose width is greater than 2^'. 
Case B. Flue greater than 16" diameter and less than 40": 



FT 



P = 

(J 

Case C. Flues greater than 40": 

P = j[j^ [Rankine uses 80,600] 

Case D. Corrugated flues, y^g" thick or thicker, and the corrugations IJ" deep, 
6" pitch: 

14,000 X T 



D 



In these formulae 



1760 
D 



T = thickness in inches ; 

P = allowable pressure in lbs. per square inch; 

C = constant 0.31; 

D = diameter in inches ; 

L = length in feet (not over 8'). 

These were supplemented in January 1894 by adding: 

THICKNESS OF MATERIAL REQUIRED FOR TUBES AND FLUES NOT OTHER- 
WISE PROVIDED FOR. 

"9. Tubes and flues not exceeding 6 inches in diameter, and made of any required 
length; and lap-welded flues required to carry a working steam-pressure not to exceed 
60 lbs. per square inch and having a diameter not exceeding 16 inches, and a length 
not exceeding 18 feet; and lap-welded flues required to carry a steam-pressure exceed- 
ing 60 lbs. per square inch, and not exceeding 120 lbs. per square inch, and having 
a diameter not exceeding 16 inches and a length not exceeding 18 feet, and made in 
sections not exceeding 5 feet in length, and fitted properly one into the other, and 
substantially riveted ; and all such tubes and flues shall have a thickness of material 
according to their respective diameters, as prescribed in the following table* 



Outside 




Outside 




Outside 




Outside 






Thickness 




ckness 




Thickness. 




Thickness. 


Diameter. 




Diameter. 




Diameter. 




Diameter. 




Inches. 


Inch. 


Inches. I 


ich. 


Inches. 


Inch. 


Inches. 


Inch. 


1 


.072 


2f 


109 


5 


.148 


12 


.229 


u 


.072 


3 


109 


6 


.165 


13 


.238 


u 


.083 


3i 


120 


7 


.165 


14 


.248 


If 


.095 


3^ 


120 


8 


.165 


15 


.259 


2 


.095 


31 


120 


9 


.180 


16 


.270 


2i 


.095 


4 


134 


10 


.203 






2h 


.109 


H 


134 


11 


.220 







FIRE-TUBE BOILERS EXTERNALLY FIRED 99 

"10. Lap-welded flues not exceeding 6 inches in diameter may be made of any 
required length without being made in sections. And all such lap-welded flues and 
riveted flues not exceeding 6 inches in diameter may be allowed a working steam- 
pressure not to exceed 225 pounds per square inch, if deemed safe by the inspectors. 

" 11. Lap-welded flues exceeding 6 inches in diameter and not exceeding 16 inches 
in diarheter, and not exceeding 18 feet in length, and required to carry a steam- 
pressure not exceeding 60 pounds per square inch, shall not be required to be made 
in sections. 

" 12. Lap-welded and riveted flues exceeding 6 inches in diameter and not exceed- 
ing 16 inches in diameter, and not exceeding 18 feet in length, and required to carry 
a steam-pressure exceeding 60 pounds per square inch and not exceeding 120 pounds 
per square inch, may be allowed, if made in sections not exceeding 5 feet in length, 
and properly fitted one into the other, and substantially riveted. 

" 13. Riveted and lap-welded flues exceeding 6 inches in diameter and not exceed^ 
ing 40 inches in diameter, required to carry a working steam-pressure per square 
inch exceeding the maximum steam-pressure prescribed for any such flue in the 
table of section 8 of this rule, shall be constructed under the provisions of section 15 
of this rule, and limited to the working steam-pressure therein provided for furnace- 
flues; but in no case shall the material in any such riveted or lap-welded flue be of 
less thickness for any given diameter than the least thickness prescribed, in the 
aforementioned table, for flues of such diameter." 



CHAPTER V. 

FIRE -TUBE BOILERS INTERNALLY FIRED. 

65. Definition of Internal Firing. Advantages and Disadvantages of 
the Principle. A fire-tubular boiler becomes internally fired when the 
furnace with grate and ash-pit are taken within the fire-tube system 
which is surrounded by the water to be evaporated. When this is done 
by enlarging a flue or part of it, or combining a number of tubes into 
one large flue for part of their length, the water surrounds the furnace 
completely. The fire-tube and shell may be cut through on the bottom 
so that the water to be evaporated is not on the bottom of the furnace, 
but this is open to the air. As before, the metal surface in contact 
with water below the fire-flue is not efficient as a rule, and little or no 
circulation of such water occurs unless mechanically compelled. 

Flues of this furnace type will necessarily be of large diameter; they 
will therefore have to be supported or stiffened by rings at short inter- 
vals, or by corrugation against collapse from external pressure, or by 
cross-tubes, or both (paragrafs 61, 63). The pressure within them is 
that of the atmosphere or less, and surrounding them is the full steam- 
pressure. If the flues are made of other than arched or cylindrical 
elements, the problem of keeping them in shape becomes more 
comphcated. 

The advantages of the principle of surrounding the fire as well as the 
hot gases by water and the flue-metal are: 

(1) Economy. No heat is lost by radiation from brickwork external 
to the boiler and heated by the^ ,heat of the fire. The water to be 
evaporated intercepts all radiation. 

(2) The part of the boiler exposed so as to radiate heat to external 
air is no hotter than the water and steam within it. Loss by radiation 
is lessened here because of the lower temperature of the radiating body. 
This makes fire-rooms more comfortable, especially on board ship or in 
contracted quarters, and is of great importance in railway practice, 
where the boiler must be exposed to cool outdoor air. 

(3) The metal surfaces surrounding the fire are most efficient evap- 
orating surfaces. This makes such boilers compact with a given evap- 
orative capacity, so that great evaporation is secured in a small space. 

100 



FIRE-TUBE BOILERS INTERNALLY FIRED 101 

This is of moment in locomotive and marine practice. Such boilers as 
are to be portable reap advantage from this. 

(4) The furnace being internal, the boiler requires either no setting 
or one of the simplest description. In wooden hulls the internal fire 
was a matter of great advantage in the matter of safety from fire, and 
the absence of a brick setting removes the difficulty from weight. The 
absence of setting makes such boilers portable, and fits them to be 
used where this is convenient. 

(5) No cool air infiltrates through cracks or porous places in the 
brickwork to dilute the gases and lower their temperature. Such 
infiltration may make a difference of ten per cent in efficiency in favor 
of internally-fired boilers which are self-contained. 

Apphcable to many types is the advantage: 

(6) They make steam and reach working pressure quickly, since the 
relation of heating surface is usually large, as compared with other 
forms, to the weight of water contained. This does not apply to large 
marine types holding large masses of water. 

The objections to the internally-fired type are: 

(7) The internal fire-box exposed to a pressure tending to collapse 
it inward makes a costly type of boiler. This is offset in a comparison 
of types by the saving from the absence of setting. 

(8) The efficiency of the heating-surface keeps down the temperature 
of gases, and thus prevents their complete combustion and causes smoky 
products of combustion. This is a real difficulty with coals containing 
much volatile matter, and vitiates economy of such boilers with such 
coals. Locomotives and marine boilers are usually the worst offenders 
in smoky cities. The difficulty is increased when high rates of com- 
bustion are used. Means must be used to keep the gases hot enough 
to burn. 

(9) Rapid steaming capacity secured by large heating-surface, 
coupled with a small volume of water in the boiler at one time, makes a 
type in which pressure will rise rapidly from the safe working pressure 
to a pressure so much higher as to endanger the resistance of the shell 
to rupture. This makes such boilers dangerous in proportion to their 
liability to this trouble. 

Applicable to some types are the objections: 

(10) Many types introduce places in their structure which are hard to 
clean and inspect. 

(11) Circulation is not always perfect or satisfactory, and one part 
may have water in it which is much cooler than the average or normal 
temperature. This gives rise to unequal contractions and tends to 
develop leaks. Or the steam may not be carried away from the heating- 



102 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

surface by the circulation, but may remain and keep water from touching 
and cooHng the heating-surface, so that it becomes overheated. These 
do not attach to the same types, nor is either difficulty common to all 
types. The special features of any type will appear in their proper 
places. 

66. The Cornish and Lancashire Boiler. The Cornish boiler is a 
single-flue boiler, with the fire-box or furnace at one end of it (Fig. 95). 




Fig. 95. 

The flue is therefore of large diameter (probably five tenths of that of 
the shell), and has to be stiffened against deformation and consequent 
collapse by the methods suggested in paragraf 61. The furnace is 
formed by inserting grate-bars supported on bearers across the flue, and 
its back is made by a brick bridge-wall. The gases pass backward 
through the flue to a back connection, whence they come forward 




^^s 



Fig. 06. 



FIRE-TUBE BOILERS INTERNALLY FIRED 103 

either along the sides or under the bottom if the chimney-duct is at the 
front ; but if the chimney is at the back, the gases come to the front in 
side flues and return under the bottom. Such a boiler requires to be 
set in brick (Fig. 98). 

The objection to the Cornish boiler is the large and weak flue. This 
early caused the development of the Lancashire boiler, which is some- 
times called the double Cornish boiler. Two flues with internal fires 
replace the single flue of the Cornish. Each will be of smaller diameter 
and hence stronger, and the existence of two fires permits cleaning of 
fires and coaling to be done alternately in each, with advantage to the 
steadiness of pressure. Fig. 96 shows a Lancashire boiler fitted with 
the Galloway water-tubes (paragraf 67). 

A modification of this type in which two furnace-flues join into one 
flue behind their bridge-walls has been called in England the " breeches " 
boiler. The American type of this has been seen in a form of locomotive 
boiler which the single flue serves as a combustion-chamber. The 
alternate-firing principle helps to keep up a high temperature in the 
combustion-chamber when one furnace is freshly fired with gaseous coal, 
and the distilled products are ignited before getting into the fine sub- 
division caused by tubes (Fig. 97). 

67. The Galloway Tube in Lancashire Boiler. The Cornish and 
Lancashire boilers are not usual in America, except in the modified form 
caused by introducing the Galloway tube (Figs. 96 and 98). This is a 
conical water-tube intended to cross the fine of either of the foregoing 
types, and serve both to stiffen it and to add a very efficient heating- 
surface of water-tube directly in the hottest current of the furnace- 
gases. The conical shape is given to the tube to favor circulation at 
uniform rate, but more especially to make it possible to pass the flange 
of the smaller end of the tube through the hole made in the flue to 
pass the larger end, but not its flange. By this expedient one of the 
inner tubes which fails can be cut out and replaced by working from 
without the flue and without disturbing other tubes nearer the ends of 
the flue. The tubes may be alternately vertical and horizontal, or 
they may all diverge from the vertical. The flanges of the tubes serve 
to rivet them to the flue, one inside and the other outside (Fig. 98), and 
where the tubes brace the flue no stiff ening-rings will be required. 
The flue usually has provision for flexibility in case of unequal ex- 
pansion of shell and flue (paragraf 61). 

68. The Scotch or Cylindrical Marine Boiler. — The cylindrical furnace 
arrangement of the internally-fired flue-boilers leads naturally to that 
form of boiler which is so generally used in the merchant marine. The 
large cylindrical shell will envelop or contain two or three internal flue- 



104 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 





FIRE-TUBE BOILERS INTERNALLY FIRED 



105 



furnaces, arranged as shown in Fig. 99 (see also Fig. 100). These 
furnace-flues being short are usually corrugated in modern practice 
to give them stiffness against collapse without stiff ening-rings. The 
flue is first welded lengthwise, and then corrugated IJ inches deep 
and With 6 inches between corrugations (Fig. 104). The end is flanged 




Fig. 99. 



or straight to attach it to the front or rear sheets. Corrugation increases 
enormously the resistance to deformation by pressure, and its only 
drawback is the diflSculty in keeping it cleansed outside and in. 

At the rear of the furnace-flue the gases rise in a " back connection '* 
to the plane of the tubes, still surrounded by water, whereby the heat 
of the gases is more completely withdrawn (Fig. 106) ; and from these 



106 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

tubes the gases and smoke pass into smoke-boxes and thus to the 
chimney-stack. Sometimes such boilers are made double-ended, 




Fig. 100. 



either Hke Fig. 103, or with the back connection partly in common. 
The flat surfaces of the back connection require careful staying as'well 
as the large areas of the heads. The shells are butt-jointed and double 




Fig. 101. 

or manifold-riveted, by reason of the strength required with large 
diameters (paragraf 35). Such boilers usually have through-stays and 
stay-tubes as well. 



FIRE-TUBE BOILERS INTERNALLY FIRED 



107 




Fig. 102. 



The Scotch boiler needs no setting and is self-contained. The 
objection to it is the tendency of the water below the furnace-flues 
to cool down and remain without circulation, thus preventing the 
shell from getting uniformly warm. This is prevented in part by 
causing this lower water to circulate mechanically by means of 

connecting the suction of the feed- 
pump to the lower part of the boiler, 
while its delivery or forcing connec- 
tion is toward the surface of the water 
in it. Other devices are also used for 
the same purpose, perhaps the best 
known being the hydrokineter pro- 
posed by a Mr. James Weir of Glasgow 
(Fig. 102). Here a steam jet from 
another boiler with steam up is used 
to induce the motion of the dead water under the furnaces by an 
injector action (paragraf 155). 

The typical Scotch marine boiler is intended to be laid athwartship 
and to get a length of course for the gases by a return arrangement of 
tubes. This makes a large diameter necessary. For high pressure, 
and where the boiler can be laid lengthwise, the form of Fig. 105 gives 
the necessary length for the gases to give up their heat, and keeps 
the diameter down. 

69. The Rectangular Marine Boiler. With the lower pressures 
used in the simple condensing engine rectangular fire-boxes or furnaces 
have been much used, and often the shell has been made with flat or 
arched surfaces so as to fit the lines of the vessel to a degree. The 
gases may be led from the furnace by flue or tubes to the back con- 
nection and then returned by flues or tubes to the front (Fig. 106). 
Sorr.etimes the gases were returned on a lower level (drop-return- 
tubular or flue-boilers), and many combinations have been made 
of the tube and flue principle. The type of Figs. 101 and 105 is gradu- 
ally replacing these weaker and less reliable forms as pressures increase. 
Flat-sided marine boilers are still to be seen for simple condensing 
engines in lake and river practice (Fig. 107), but even here the furnaces 
are usually cylindrical and either corrugated or stiffened with rings 
(Fig. 101). Oil or grease settling from the water upon these furnace- 
crowns and causing them to soften and come down from overheating 
is a very frequent source of annoyance and danger in boilers of this 
class, and is aggravated by unwise handUng of the engines. 

The conditions attending the use of the marine boiler in sea-going 
vessels call for a type of highest efficiency and best economy with 



108 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 






L 



It-— I — -#1 



i 






FIRE-TUBE BOILERS INTERNALLY FIRED 



109 



least bulk and weight. The vessel must carry its own coal, and have 
to spare for any delay in reaching its next coaling station. Hence 
boilers of this class stand very high as types. Domes for such boilers 
are inconvenient, and for large diameters will either be dispensed 
with as* not required where a large steam-space is furnished by the large 




Fig. 106. 



diameter, or a dry-pipe will be used. For smooth-water boats the 
steam-chimney is still much used (paragraf 49 and Fig. 106). 

70. The Locomotive Boiler. The boiler which is to supply steam 
to the cylinders of the locomotive engine must meet the most exacting 
requirements. 

(1) It must be self-contained, requiring no setting. 

(2) It must evaporate a very great weight of water in a very short, 
time to meet speed and grade resistances with heavy trains without 
such drop of pressure as will delay the train or time schedule. 

(3) It must be exposed to low outdoor temperatures and snow and 
rain. 

(4) It must have minimum bulk or volume. 

(5) It must be efficient, since the engine and tender as a unit must 
transport their own water and fuel. The internally-fired type with 
many small tubes meets these requirements best. A high rate of 
combustion on the grate must be secured (paragraf 12) to enable a 
single grate to furnish the heat required per minute or per hour, with 
consequent high temperature of fire; the tubes must withdraw this 



110 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




FIRE-TUBE BOILERS INTERNALLY FIRED 



111 



i^zh f 



heat very rapidly when the gases are passing rapidly, else the smoke-box 
and stack temperatures will be so high as to be wasteful; and combus- 
tion must not be incomplete. 

The designer is limited also by the permissible diameter of the 
exterior shell; by the limit of width for the grates; by the possible 
length over all imposed by the curves of the line, and by the limit of 
human endurance in the fireman in the amount of fuel which can be 

charged into the furnace on a run of 
a certain number of hours or miles in 
length. Furthermore, unless the 
grate area is increased, the increased 
intensity of draft to get the com- 
bustion will force mechanically so 
much fuel out unburned through 
the stack as to overburden the 
firing process and produce coal 
waste. There can be little water 
storage in the locomotive boiler to 
store reserves of heat to any con- 
siderable extent, and the pressure 
will fall on up grades and rise on 
descents in spite of the best skill 
and experience in both fireman and 
engineman. If possible the feeding 
of cold water on up grades should 
be avoided. 

The boiler being horizontal per- 
force, the general lines of the preced- 
ing figure 105 will be followed, 
except that the fire-box or furnace 
will be more usually rectangular in 
plan, and the shell will be open on the bottom below the grate to let 
ashes fall into an external ash-pit. The rectangular section was early 
imposed by the supposed compulsion to get the fire-box end between 
the frames and the large driving-wheels. This gave rise to an end- 
view like Fig. 110, which is half elevation and half section through 
the fire-box. The crown-sheet is a flat arch stayed to the shell; the 
sides which form the " water-legs " are stayed by stay-bolts from com- 
ing in. To get a large steam-space, the boiler is carried up as high 
as possible over the furnace-crown, and either is prolonged on that 
line to the front, or is drawn in by a tapering ring beyond the fire-box 
to a smaller width and height. This tapering course is called the waist 




Fig. 110. 



112 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

of the boiler, and the enlarged fire-end makes a ''wagon-top" boiler from 
the suggestion of the canvas cover over hoops in early prairie wagons. 

If it be preferred to avoid the different lengths of the radial crown- 
sheet stays of Fig. 110 and their different expansion under heat and 
stress, the flat crown-sheet and straight-side fire-box will be designed 
(Fig. Ill), and either limited in width to the space over the frames 
between the wheels, or for small diameter driving-wheels carried over 
the latter also (Figs. 112, 113). If finally the wheels can be moved 
enough forward and nearer the center of gravity to get the fire-box 
behind the wheels altogether, the lateral limitations are removed, 
and the design of Fig. 114 becomes possible, limited only by the 
clearance width between two engines on parallel tracks. Fig. 115 shows 
the back-head in the Belpaire design strongly and rigidly stayed by 
gusset-stays. 

In the illustration the fire-box is reached through the back by one 
door. If the fuel is to be anthracite in very small sizes, even the wide 
grates shown will compel too rapid a combustion rate, and a specially 
wide furnace with two doors of access will result (Fig. 116). The ash- 
pit only comes down between frames, and the cab is moved in front 
of the fire-box altogether. These extra wide fire-boxes were first brought 
out by a Mr. Wootton of the P. and R. Railway, and when made very 
long also (Fig. 117) have to allow an axle to come up pretty close to 
the top of the ash-pit. 

The extra wide fire-box end shown in Fig. 114 will serve as a favorite 
type of locomotive boilers intended for stationary use, where the type 
is that best adapted for the service, but the limitations of the line are 
not imposed. 

With the softer or bituminous coals, the rapid rush of flame into the 
tubes is not favorable to economical combustion. To give chance for 
flame combustion to be complete and at high enough temperature, 
fire-brick is introduced within the fire-box (Figs. Ill, 115) or behind 
it (Figs. 117 and 118) to provide for such time and temperature as is 
required. 

The illustrations also show the various types of crown-sheet bracing, 
either the crown-bar system of Fig. 112 for flat crowns, or the curved- 
bar and sling-stay system of Fig. 114 as substitutes for the radial bolt 
of Figs. 110, 113, and 117 of the arched-top types. They show also the 
straight and sloping back-head, and the method of constructing the 
fire-door opening through the latter in which the two plates are flanged 
inward to overlap and then riveted together. Or the space between 
plates at the opening may be closed by a soHd forged ring like the 
"mud-ring" which closes the bottom of the water-legs around the 



FIRE-TUBE BOILERS INTERNALLY FIRED 



113 




114 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 





FIRE-TUBE BOILERS INTERNALLY FIRED 



115 




116 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

fire-box. Or, again, a ring may be made of U-section of plate of the 
shape of the opening and riveted to both surfaces. The mud-ring is 
almost universal for road-locomotive boilers; for stationary use, the 
inner plate may be flanged outward and downward to form the closure 
of the water-leg and joint with the outer sheet. 

These boilers also all show the '' extension front " smoke-box which 
enables the desirable spark-arrester or netting to be placed here below 




Fig. 116. 



the orifice of the exhaust-nozzle (Fig. 111). The draft in the fire-box 
and tubes can also be damper-regulated without putting back-pressure 
upon the engine pistons, and the smoke-box can be used as a holder 
for sparks and cinders which can be conveniently removed at the end 
of a run. 

71. The Locomotive Boiler with Corrugated Furnace. The application 
of the corrugated cyhndrical flue to the locomotive after it had proved 
its advantages in marine practice has been made by Mr. George S. 
Strong and by Mr. Cornelius Vanderbilt, Jr. Fig. 119 shows such a 
boiler with three furnaces taking into a common combustion-chamber. 
From the front of the latter the tubes run to the smoke-box. The 
furnaces need no staying on either tops or sides, but the combustion- 
chamber with flat-top element is stiffened by crown-bars and hung by 
sHng-stays. The ash-pits are troublesome to clean when coal is used 
as a fuel, and hence the single furnace is more usual. The design 



FIRE-TUBE BOILERS INTERNALLY FIRED 



117 




118 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




-gi- 



] 



FIRE-TUBE BOILERS INTERNALLY FIRED 



119 



shown is intended for use with oil-fuel, and this limitation is not present. 

Fig. 120 shows a fire-box with corrugations upon the plane elements. 

This is due to Mr. WiUiam H. Wood. Table VIII gives some data on 

the large locomotive boilers which have been illustrated, and on some 

others. 

TABLE VIII 



Fig. 


Builder. 


Railway. 


Type. 


Boiler 
Pres- 
sure, 
Pounds 


Cylinders, 
Diameter and 
stroke, Inches 


Diam- 
eter 
Drivers 
Inches. 


Weight 

on 
Drivers, 
Pounds. 




Am. Loco. Co. 


N. Y. Central . . . 


4-4-2 


200 


21X26 


79 


95,000 


113 


Am. Loco. Co. 


Penna. R. R. 


4-4-2 


205 


20iX26 


80 


109.000 




Am. Loco. Co. 


C. R. R. of N. J. 


4-4-2 


210 


20^X26 


85 


99,400 




Am. Loco. Co. 


Nor. Pacific 


4-6-2 


200 


22X26 


69 


134,000 




Bald. Wks . . . 


C. R. R. of N.J. 


2-6-2 


200 


18X26 


63 


108,000 


112 


Bald. Wks.... 


Chicago & Alton 


4-6-2 


220 


22X28 


80 


141.700 




Am. Loco. Co. 


C. B. «& Q 


2-8-0 


210 


22X28 


57 


187,000 


114 


Bald. Wks . . . 


B.W. &Gt. Falls 


2-8-2 


200 


14+24X26 


50 


128,000 


119 


Bald. Wks . . . 


A. T. & S. F.... 


2-8-0 


210 


17+28X32 


57 


191,400 











Ratio 
















Heat- 


Heat- 


of 












Fig. 


' Weight, 
Total Lbs 


mg 
Sur- 
face 


ing 
Sur- 
face, 


Heat- 
ing 
Surface 


Tubes, 
Num- 


Tubes, 

Length 

Feet 


Grate 
Area, 


Per cent 

of Fire-box 

to Total 


Fuel. 






Fire- 


Total 
Sq. Ft. 


to 
Grate 
Area. 


ber. 


and 


Sq. Ft. 


Heating- 








box. 
Sq. Ft. 




Inches. 




Surface. 






176,000 


180 


3,505 


70 


396 


16 


50 


5 1 


Bit. Coal. 


113 


176,000 


166 


2,640 


47 


315 


15-1 


55 5 


6 2 


Bit. Coal. 




191,000 


174 


2,967 


36 


325 


16-6 


82 


5 86 


Fine Anthracite. 




202,000 


175 


3,462 


74 


301 


18-6 


47 


5 


Bit. Coal. 




165,000 


137 


1,832 


33 


249 


13 


54 5 


7 47 


Anthracite. 


112 


219,000 


202 


4.078 


75 


328 


20 


54 


4 95 


Bit. Coal. 




208,900 


195 


3,827 


70 


462 


15 


54 


5 


Bit. Coal. 


114 


166,900 


174 


2,496 


44 


270 


16-6 


56 


6 97 


Lignite. 


119 


214,600 


165 


4,266 




652 


13-7 





3 86 


Oil. 



72. Derivatives of the Locomotive Boiler. The locomotive boiler 
received its type form from Stephenson at the successful competition 
in England in 1829. Its excellences in the way of rapid steaming, 
compactness, and economy have made it the starting-point of many 
modifications of type for stationary use, and it has also been adopted 
in torpedo-boat conditions. Fig. 121, for example, is a short, self- 
contained, non-radiant form without lateral water-legs, but a brick 
lining in both furnace and back connection. This fits it for economic 
use with bituminous or flaming coals. 

In Fig. 122 a type of circular fire-box, combustion-chamber, and tube- 
nest is used without stays and their attendant cost and objections. 



120 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

The whole fire-tube element can be removed for renewal without dis- 
turbing the shell or connections by cutting off the tubes and removing 
the front head. 

These secure structural cheapness and the basal features of their 
type, for stationary use. The same excellences attach to Fig. 123, in 
which the furnace is corrugated with tubes leaving a tube-sheet at the 




Fig. 121. 



rear and leading into a surrounding casing of sheet steel lined with 
asbestos air-cell blocks. The water rises from the lower cylinder through 
necks into the water and steam-drum above, and is led off as steam 
from the perforated dry-pipe. The boiler carries its own setting and 
combines the features of external and internal firing. 

73. The Upright Boiler. If the internal furnace of the Cornish type, 
or the marine type of Fig. 105, or the circular furnace type of Fig. 119, 
locomotive type, or Fig. 122 of the derived type, be any one of them 
turned up on end so as to make the tubes rise vertically from the crown- 
sheet over the fire, such a vertical boiler then becomes the upright 
(Fig. 125). The water surrounds the fire-box as before, and the latter 
is easily stayed to the cyhndrical shell. The steam now, however, 
goes to the upper end, and the upper ends of the tubes traverse the 
steam-space above the water-hne. Crown-stays disappear because 
much pressure is removed from the crown-sheet by the tube area, and 



FIRE-TUBE BOILERS INTERNALLY FIRED 



121 



the tubes stay much of the upper head. The water-legs are inaccessible 
except through hand-holes, and the crown-sheet filled with closely 
arranged tubes is hard to clean inside. There is no place for a dome 
or dry-pipe. 





Fig. 122. 

The features of the upright type are: 

(1) It is Ught and portable. 

(2) It requires no setting for the general type shown in Figs. 125, 

(3) It is a rapid steamer, because vertical tube-surfaces evaporate 
rapidly and the water is subdivided. 

(4) It takes little floor-space. 



122 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 
(5) The upward motion of the hot gases is the natural flow of such 



(6) The simpUcity of the stays makes it a cheap boiler. 
On the other hand, it may be urged: 

(7) The circulation is not determinate, and may be defective. 
Everything tends to ascend all over, and if water does not replace the 
steam made at the tube-sheet, the latter will overheat. This is reme- 




FiG. 123. 



died in part by thinning out the tubes, so as to leave open spaces for 
water to move through, and by the use of baffle-plates or brattices to 
force a determinate circulation. 

(8) It is troublesome to get a dome or a large steam-space. Wet 
steam will result if the flow is rapid. 

(9) The upper ends of the tubes are not water-cooled in such a 
design as Fig. 125, but will grow very hot and expand so as to cause 
leaks at the upper tube-sheet. While such hot tubes may serve to dry 
the steam somewhat, the difficulty from unequal expansion is of suffi- 
cient moment to justify the design of Fig. 127, where the smoke-box 
is drawn down into the boiler proper to submerge or drown the ends 
of the tube below the water-line. 

(10) The boiler cannot be entered for a personal inspection, and 
cleansing is not easy when it has to be done from outside. This is a 
very serious objection with many waters. 

(11) It holds the least amount of water of any of the shell types, 
which makes it pass quickly from safe pressure to one which would 
endanger it. This danger is greater the smaller the boiler. 



FIRE TUBE BOILERS INTERNALLY FIRED 



123 




Fig. 125. 



Fig. 126. 



124 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




Fig. 127. 



FIRE-TUBE BOILERS INTERNALLY FIRED 



125 




Fig. 128. 



126 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

74. Modification of the Upright Boiler. To secure the convenience 
of the upright arrangement and at the same time avoid some of its 
defects, various special designs have been advanced. Fig. 126 is the 
Manning boiler, designed to secure a larger grate area and either a 
slower combustion rate or the consumption of more fuel than with the 
type form, and derive the advantage of reduced ground-plan for a 
required evaporative capacity. The upper ends of the tubes act as a 
superheating surface to dry and superheat the steam surrounding 



MAN HOLE 



>oO°o°o°°ooooV 

-OOOOOOGOOOOO 



HAND HOLE 






or o^ Oq^ 




HAND HOLE 



Fig. 129. 

them, and the tube is long enough to compress or yield slightly under 
unequal expansion stress without starting the tube-sheet joints. In 
Fig. 127 the water-line is carried above the level of the upper tube- 
sheet, drowning the tubes under water and lessening the HkeUhood of 
working the expanded joints. The smoke-box cone is, however, ex- 
posed to collapsing stress from without and to high temperatures from 
within. It requires radial staying. Fig. 128 is the Corliss boiler, using 
an annular grate with several fire-doors in its brick setting, the grate 
surrounding a mud-drum. Above the upper tube-sheet, or in the base 
of the chimney as it were, is a steam dome surrounded by the hot gas 
and forming a superheating element. The water can be carried so 
near the top of the barrel that overheating of the tube-ends is secondary. 
Fig. 129 shows the Reynolds boiler arrangement of tubes in such 
fashion that through a manhole full access is given between the rows 
to every part of the crown-sheet (Fig. 129). 



FIRE-TUBE BOILERS INTERNALLY FIRED 



127 



75. The Fire-engine Boiler. The boiler for the steam fire-engine for 
municipal use must meet the prime necessity of Hght weight so that 
by horses or by its own motor 
it shall be rapidly run to the 
fire over paving or roads of 
ordinary sort. It must also get 
up steam to working pressure 
within three minutes in well- 
equipped cities if horse-drawn, 
or must have propelling steam- 
pressure to start with if self- 
propelled. The upright boiler 
meets the first and second 
requirement the best of any fire- 
tube boiler, and until the 
development of the water-tube 
types it was the only one in use. 
It was a submerged or drowned- 
tube type, such as Fig. 127 or 
Fig. 130, with copper or brass 
tubes as close together as they 





Fig. 130. Fig. 131. 

could be placed, and working with strong forced draft by steam jet. 
The later and other types are usually composites to avail of the 



128 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

advantages of the water-tube type as respects quick-steaming. 
Fig. 131, for example, has both fire-tubes and water-tubes, the latter 
drawing water downward in the water-leg and passing it upward 
as steam at the upper tube-sheet, while the hot gases pass through 





Fig. 132. 



the fire-tubes and out at the top. The low water-line makes the fire- 
tubes mainly superheating surface, the steam being made really in 
the water-tubes. 



i 



FIRE-TUBE BOILERS INTERNALLY FIRED 129 

76. Combinations of Type. Fig. 132 is also a boiler for fire-engine 
service primarily in which the fire-tube and water-tube principles are 
combined as in the form just referred to. The special type here is the 
Field tube (Fig. 6, paragraf 23), in which rapid circulation and self- 
cleansing are secured when the boiler is at work. It has been used 
also in tugs. Similar combinations have been made by putting water- 
tubes at the sides of an ordinary brick fire-box between the grate 
and the wall (Smith's); or by putting such water-tubes in the combus- 
tion-chamber behind the fire (Stead's). There are also unclassifiable 
propositions, such as that of mounting the horizontal shell upon trun- 
nions, as the Corliss boiler would be (Fig. 128) if turned horizontal, and 
causing such cylinder to revolve slowly with little water covering a 
part of the tubes only (Pierce's). These belong to the specialist and 
the historian rather than to the practical student, and this place is 
made for them rather in the logic of the subject than because they 
are of practical import. 



CHAPTER YI. 

WATER -TUBE BOILERS. 

80. Introductory. In paragraf 51 of Chapter III the two directions 
of development were pointed out. The one sought to subdivide the 
fire elements and surround small units of heat-carrying metal with the 
water in relatively undivided masses. The other development has 
been to subdivide the water-containing metal vessel into small units, 
while the fire and gas were in larger and integral masses. Instead of 
keeping a large kettle of water, and passing small currents of gas in 
tubes through the water, the tendency has been to multiply small 
kettles in the one fire. These kettles must all be connected together 
at some point — or at more than one — in order that they may deliver 
the steam they make into a common delivery pipe; and they must be 
supplied with feed-water from a common source. As the kettles must 
contain the water, and the fire be outside of them, such units, if tubular 
in shape, will be properly called '' water-tubes." They must all of 
necessity be in an externally-fired class when the tube is small. 

When these separate water-heating or steam-generating water-tube 
units act independently as steam-boilers and are grouped together as an 
aggregation to deliver their steam into a common steam-space or at a 
common disengagement area, the boiler as a whole becomes a sectional 
boiler. There have been water-tubes externally fired in the previously 
discussed forms (Galloway, paragraf 67 ; Fire-Engine, paragraf 75), 
and the water-tube principle was used in old navy practice with rec- 
tangular shells (paragraf 69); but here there was retained the en- 
veloping shell within which these water-tubes performed their work. 
Only a part of the heat from the fire entered the water by way of the 
water-tubes, or these water-tubes were only part of the heating-surface. 
When the heating-surface is largely or exclusively made up of such 
water-tubes or other generating units, and the large-diameter enveloping 
shell disappears from around such units, the boiler becomes a sectional 
boiler. The forms of generator in which this water-tube principle has 
been embodied are: 

(1) The Plain Cylindrical Boiler. (3) The Sectional Boiler. 

(2) The French or Elephant Boiler. (4) The Coil or Pipe Boiler. 

(5) The Flash and Semi-Flash Boiler. 
130 



WATER-TUBE BOILERS 



131 




132 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

81. The Plain Cylinder Boiler. The discussions in paragrafs 23, 25, 
and 51 have estabhshed the cyhnder mth hemispherical or flat heads 
as the better shape than the spherical for receiving the heat of the fire 
and storing such energy in the form of pressure (Figs. 10, 25, 50, and 69) . 
But when the temperature of the fire increases in an effort to burn the 
coal more rapidly and make more steam or at higher pressure, the only 
possible way to secure area of contact to absorb such heat is to lengthen 
the cylinder of the boiler. The same is required when the length of the 
flame becomes great with flaming or gaseous coals. The old solution 
(Figs. 7, 135) was to flex the gas or flame-current back around the sides 
of the boiler — the '^ wheel-draft " of historic settings — when the 
pressures were low. Such lengthening makes an expensive setting in 
the brick which supports the boiler and forms the external flues, and 
occupies ground-space which may be costly or prohibitory. If at the 
same time that length is demanded, it is desirable that storage capac- 
ity for heat in the ^ater be supplied; and if it be also sought to increase 
the diameter of the shell, then the weight of the mass of water makes 
the stresses on the shell inconveniently great as respects its support. 
A trend of solution for the very long boiler for long-flame gas is shown 
in Fig. 134, where first the long cylinder is hung from equalizing levers 
pivoted at the center of each so as to distribute the load equally at 
each of the four points of support on the shell; and secondly by 
doubhng the cylinder capacity by the water-drum connected to the 
upper cyhnder by necks or nozzles. A second solution was to break 
the long cylinder into two halves (Fig. 136) at or near the middle, 





R 


R 


R R 


R 




1 


\ 




~rr 


1 


\ 



a^ 



i^^ 



□ 



Fig. 136. 



supporting each half at two points and coupling the two for steam 
and for water by flexible copper connections which would yield slightly 
as the boiler tended to flex upon its supports. Such boilers had the 
advantage of simplicity in construction, and access for cleaning was 
complete. They were bulky and not economical. 

83. The Elephant, Union, and French Boiler. If now the principle 
of Fig. 134 of a double-deck arrangement of superposed cylinders be 
carried out in a shorter length of axis to get surface and storage without 



WATER-TUBE BOILERS 



133 



excessive length but by increase of diameter, the type known in the 
United States as the Elephant boiler results (Fig. 137). Less area in 
ground-plan is required, but more height ; the cylinder diameter of each 
unit becomes less than if that same water capacity had been secured 
in one shell of the given length, and hence the shell is stronger against 
rupture (paragrafs 24 and 25) from internal pressure. If the boiler 
C in Fig. 137 was fitted with fire-tubes, as was quite a common 




Fig. 137. 



practice for non-flaming fuels, the composite was called a Union boiler; 
or the two or three necks uniting the elements C and D might again 
be replaced by an enveloping shell of plate connecting the upper and 
lower cylinders along a larger area of the elements of both shells. 
This is no longer in use. 

When instead of one lower element C in the Elephant type, a pair 
or three smaller cylinders were placed below the main shell as in Fig. 
135, the type becomes the French boiler, much used in industrial 
France, where it originated. It reaps the advantages of large water- 
content with small shell diameter, and increased heating-surface due 
to the double travel of the gas. The circulation in all forms of double 
boiler is indeterminate and variable after steam begins to form in the 



134 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

lower boiler, and such steam has to make its way through a great 
vertical height of water to find its disengagement area. 

But by the multipUcation of cyhndrical units, the trend of develop- 
ment toward the sectional principle has been started, and its attendant 
advantages. What is the sectional principle, and what are its advan- 
tages and disadvantages? 

83. The Sectional Principle. The principle of the sectional boiler 
is not the same thing as the actual construction of the generator which 
embodies it. There are advantages and disadvantages which are 
secured or missed by certain forms more than others. A sectional 
boiler is a steam-generator in which the plan of a single enveloping 
shell to contain the water and steam is abandoned and is replaced by 
that of a number of small generating vessels so joined together that the 
steam formed in all of these separate units or sections is delivered from 
a common disengagement surface into a common steam-space. The 
sectional principle may be carried in a boiler of large capacity to the 
extent of subdividing the disengagement area, so that the steam from 
several such areas shall be delivered inlo a common steam-drum, from 
which it shall be withdrawn by the steam-pipe. 

The generating vessels in the forms to be discussed hereafter will 
be found to be tubes either straight or curved, and inclined at small 
angles from the horizontal or vertical plane. The only exception is 
the Harrison sectional boiler (Fig. 138), made up of cast-iron or cast- 
steel spherical or spheroidal units jointed on three or four or six faces 
to other similar units, forming in effect tubes or banks of spheres which 
deliver their water and steam at an upper disengaging area. When the 
water-tubular units become of small diameter, and instead of connecting 
at one or both ends into transverse headers such generating elements 
become a continuous coil of pipe, or a combination of pipe and fittings, 
the name sectional is less easily applicable, and the boilers become 
coil or water-tube generators. When the coil or pipe is used as a 
flash or semi-flash generating surface, the name sectional or coil is again 
not used, but its flash property is emphasized. 

84. Advantages of the Sectional Principle. Among the advantages 
derivable from the use of the sectional principle may be listed: 

(1) By subdividing into sections, each section has a small diameter, 
or one much less than that of the shell of the shell boiler. Strength 
to resist rupture with a given internal pressure increases as the diameter 
is less (paragraf 207). Hence each section is far safer against rupture 
than the large shell with same thickness of metal, and the danger from 
explosion of the boiler is much more remote. 

(2) The rupture or failure of any one of the units from overpressure 



WATER-TUBE BOILERS 135 

or deterioration from any cause should not and usually does not cause 
the failure or loss of the whole structure. The failure of the unit should 
act as a safety feature, whereby pressure is released at one place only 
and before the other units are involved in any serious overstrain. 
Furthermore, the repair of any unit or section makes that part as good 
as new, and in this way the parts of the boiler may be gradually replaced 
and the whole structure become really new. It is, therefore, the 
safety of this type of boilers which has given it the great development 
of recent years as the pressures of steam have been increasing. The 
safety is not from the avoidance of all possible harm which a rupture 
may entail. The injury from escaping steam or hot water may be 
as fatal in either case. But the sudden release all at once of the enormous 
energy stored in the water of a boiler is much less likely to occur, and 
the train of disaster is avoided which would usually follow in the case 
of a similar failure of a large shell. 

Since the great reduction in diameter which comes when the units are 
tubes would give unnecessary strength if the same thicknesses were used, 
it is more common to have thinner metal for the tubes. Hence follow: 

(3) Lighter weight for a given evaporative capacity. 

(4) Thinner tube-metal in the fire or gas-currents makes rapid 
transfer of heat to the water to be evaporated, so that the heating- 
surface is efficient, or a less number of feet of heating-surface becomes 
permissible, though not always advisable. 

(5) The sectional construction makes the boiler portable and manage- 
able so as to be put conveniently in places where access is difficult. 
The shell boiler must be handled as a whole, or built in place, if the 
doors or openings in walls are not large enough to pass it in or 
out as a whole. Sectional boilers can be put under finished buildings, 
or can be shipped beyond rail or water transportation and there 
assembled. 

(6) Repairs and renewals are easy, cheap, and rapid, and can usually 
be made b}- available labor and skill, and entail but a short stoppage 
of the plant. 

(7) The mass of the boiler which receives the action of flame and 
heat is less than in shell boilers. 

(8) Sectional boilers can be driven further above their nominal 
capacity than shell boilers. In the horizontal tubular type such 
driving may be carried a little over 10 per cent; in sectional types 
it may be over 50 per cent excess, and even for a while as high as 100 
per cent. 

85. Disadvantages of the Sectional Principle. The sectional principle, 
however, offers certain disadvantages, also irrespective of the method 



136 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

followed in applying it; but the degree in which any given form suffers 
from them may be different. 

(1) The aggregation of units must be connected together steam 
and water-tight under pressure. Unequal expansion (or contraction) 
of different parts or units must strain or loosen these joints, or flex or 
distort those parts whose length is changing, or wrench those to which 
they are attached if rigidly fitted to them. Efforts to mitigate this 
evil have given rise to the curved tube for the unit, instead of the 
straight tube, and underlie some forms of flexible connections for the 
units. 

(2) The small unit principle precludes the idea of immediate personal 
access to the inside of the tube-surfaces for cleansing and inspection. 
This must be reached in some way or other in any form of generator 
which is to be properly called a safety-boiler. Hence there has resulted 
a prevalence of straight-tube units, to which access can be had from the 
end through a proper cap or hand-hole lid, and there is usually a cap 
at each end, in order that inspection 'of the inside of the tube may be 
made with the eye at one end of the tube and a light or torch or candle 
at the other. The cap feature is also a necessity if a tube is to be 
renewed without dismounting adjacent ones. 

The objection to the cap feature is the multiplication of joints^ which 
must be faced or ground joints so as to be tight without gasket or 
packing, and which are an occasion of leakage, and therefore of corrosion, 
when not attended to most carefully. The multiple-joint objection 
belongs also to some types which have no caps. 

(3) The necessity for combining the evaporation of several tubes or 
units into one common duct or header, which is present in most of the 
types, makes the effective disengagement surface become only that 
part of the water-surface which is near the outlets of these headers. 
The disengagement is therefore tumultuous at such points when the 
boiler is driven, and water-gauges applied near such parts may show a 
fictitious water-level; and if the steam-outlet has to be near such part 
of the drum, the boiler is likely to prime. 

(4) The circulation of the currents of water in any boiler is due 
partly to the presence of steam-bubbles, which are lighter than the 
hottest water, and partly to the action of the less warm water, which is 
heavier than the hottest water. In a shell boiler this circulation is 
untrammeled by any narrow passages where high velocity is called 
for. In the sectional types the circulation must be determinate; and 
if all units are to be full of soUd water, the descent of cooler water must 
be just as fast and positive as the ascent of the steam-gas bubbles to the 
surface of disengagement. Where friction or scale or bad design 



WATER-TUBE BOILERS 137 

prevents this free descent of heavier water, and where steam formed in 
the units displaces water but cannot itself escape to the steam-drum, 
the unit becomes overheated and oxidizes and corrodes, and its over- 
heating lengthens it unduly and produces the difficulties discussed above 
under (3). 

Defective or impeded circulation with waters which deposit scale 
causes the scale to settle in the tubes or units, causing them to overheat 
and lengthen and produce the same trouble. Grease or oil depositing 
on the upper elements of tubes produces the same result. 

(5) Since the water is within the tube or unit, with pressure on it, 
the failure of such tube or unit compels the whole structure to be put out 
of use for the repair. When a fire-tube fails, a plug of pine wood can 
be fashioned for each end and securely driven home from without. 
The leakage swells the wood and keeps it tight, while preventing the 
wood from burning further than a protecting thickness of charcoal on 
the outer surface. Such plugs will last for months if a shut-down is 
inconvenient. 

Furthermore, where tubes are attached in nests or groups, the repair 
to a middle one can only be done by removing those tubes which are 
outside or around it and which may not need to be removed for any 
other reason. This consideration has dictated the prevalence of the 
straight-tube type arranged in essentially parallel rows, and with free 
space in the line of the tubes endwise. 

(6) Tubes or units which are so shaped or fitted that they cannot be 
inspected inside by the human eye for their entire length, or which are 
so curved that cleansing by scraper is uncertain or even inconvenient, 
are to be objected to or condemned outright, for many conditions if not 
for all. 

(7) The gases pass too rapidly through the necessarily limited 
length of the tubular units, and leave the setting at too high a 
temperature, without having given all their available heat to the 
water. 

(8) The workmanship and parts of the sectional boiler make it costly, 
per unit of capacity, as compared with the fire-tube shell boiler. While 
prices vary, the sectional is apt to cost from one and one-half times to 
twice as much as the shell boiler, or from $11 to $18 per horsepower, 
with an average of $14 or $15 in large sizes. 

86. Classes of Sectional Boiler. The sectional-boiler principle may 
be attained in many ways, but they will group themselves for exam- 
ination into a small number of classes. 

First, the units may be spherical or tubular. There are few examples 
of spherical units; the other class is more prevalent. 



138 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

The tubular class may include: 

(1) Straight tubes. 

(2) Tubes curved at ends, straight in middle. 

(3) Tubes curved for their whole length. 

(4) Closed-tube types. 

The straight-tube class may have the tubes inclined at about 15° 
from the horizontal, or inclined from the vertical, so that they are 
sometimes called, respectively, horizontal or vertical tubes; and the 
curved-tube classes pass into the coil type when the curvature becomes 
continuous for any one tube for more than 360°. 

These several types in practice are identified by their builders' or 
originators' names. The predominance of one type over another is 
so often in any one locality a matter of business enterprise or commercial 




Fig. 138. 

achievement, and the improvements on each type are so much con- 
ditioned upon a leading personality in each period of use, that it be- 
comes unsatisfactory to treat of the individual types by name or at 
length. Certain typical forms alone are presented. 

87. Spheroidal Unit Type. In Fig. 138 is shown the detail of a 
sectional boiler built up of spheroids. These were of cast iron 
with flanges in the earlier forms, and latterly of steel castings of 



WATER-TUBE BOILERS 



139 



Bessemer metal. These each have circular openings which fit similar 
openings in the units above and below them, making a metal-and-metal 
rabbet-joint. The series of units is tied together lengthwise and cross- 
wise by wrought-iron tie-rods, which come out through the cap which 
closes the last openings in any series. These tie-rods not only provide 
the strength to resist the tendency to separate, and furnish a flexibility 
for the connections, but also under excess of strain they will stretch 




Fig. 139. 



enough to cause the joints of the units to leak and relieve some of the 
pressure. The wrought iron also gives to the cast-iron whole some of 
the properties which cast iron would lack if used alone or altogether. 
The boiler has some surface in the steam-space exposed to hot gases, 
which gives a superheating area which tends to dry the steam when 



140 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

the boiler is working slowly. It offers some of the disadvantages 
discussed in paragraf 85. 

88. Vertical Straight Open-tube Type. As an example of subdivided 
generation in straight vertical tubular units open at both ends, Fig. 139 
may be cited. Four-inch tubes are expanded into molded nozzles in 




Fig. 140. 



the mud-drums below and the steam and water-drums above. Both 
sets of horizontal drums are cross-connected. The fire in a Dutch-oven 
type of furnace where the radiant fuel is not cooled by the boiler-surface 
sends its gases up the right-hand section and down and out to the 
chimney on the left. Baffles force the hot gas into intimacy with the 



WATER-TUBE BOILERS 141 

tubes. The descending current is at the cooler left-hand half and is 
determinate and effectiva The drums do not touch the brick of the 
setting, enabUng inspection to be satisfactory. The tubes are so 
spaced that a defective inner one can be removed and replaced without 
disturbing the others by working from within the drums. The whole 
boiler rests on the castings at the bottom and the vertical walls are 
inclosing flues. Scale is not likely to settle in such vertical tubes but 
in the drums below the circulating pipes. 

In Fig. 140, there is no return of the gases, but they pass up through 
a sort of steam-chimney which is surrounded by steam. Here the 
circulation is made positive, definite, and powerful by a descending pipe 
outside the setting altogether and not exposed to action of heat. The 
lower drum acts as a mud-drum below the circulation pipe. As in the 
previous case, defective or injured tubes must be withdrawn and replaced 
through the gas-channel in the center. Unequal expansion is not 
supposed to occur, by reason of the unlikelihood of scale settling on the 
vertical surfaces. Inspection is done from the upper and lower drums, 
which are large enough to admit of entry; and the tubes being open and 
free above and below, they can be seen throughout tlieir whole length, 
and cleaning apparatus can be introduced and effectively used. Expan- 
sion of the chimney-plates is permitted and favored by the flanged 
ring-joint. The disengagement from each tube is free at the top and 
independent of all the others. 

89. Horizontal Straight Open-tube Type. The name horizontal is 
intended to include the types in which the generating tubular units are 
inclined at comparatively small angles to the horizon. The elevation 
of about 15° at one end both favors the circulation and compels it to 
be definite, and also makes room for the fire-box, in many of the types. 
The greater length of the water-column at the back end of the boiler 
gives the weight of solid cooler water by which the water and steam- 
bubbles are forced upward, at the front or over the fire. 

In Figs. 141, 142, and 143 is presented the type which has the least 
sectional features. The generating tubular units are expanded into 
the inner plates of two water-legs of steel plate front and rear. These 
legs are flanged at the top and connect to the steam and water-drum 
above. The legs are stay-bolted. Opposite each tube at each end is 
a cap over a corresponding hole in the outer plate, so that any tube 
can be removed and replaced endwise. Expansion of any tube by heat 
more than its neighbors has to be taken up by bending of the tube or 
by compression which strains the joint with the water-leg. The leg 
is too stiff and strong to bend, and is held by the other tubes. Scale 
and oil render the horizontal tube liable to overheating, or any cause 



142 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

which prevents intimate contact of water and the tube-metal exposed 
to heat. 

In Fig. 144 a side section is presented of a type of wide-spread accept- 
ance. The generating water-tube units are in banks or nests of seven 




Fig. 141. 



staggered vertically (Fig. 145) expanded into a steel header (Fig. 147). 
This header has the hole and necessary cap opposite the tube for inspec- 
tion, cleansing, and renewal (Fig. 146), and all the steam made in the 




Fig. 142. 



bank of tubes rises to the disengagement surface through the connection 
at the top of the header. This makes the circulation through that 
upper neck so rapid as to be tumultuous, and makes it desirable to 
take the steam away from the boiler at its back end. The water-level 



WATER-TUBE BOILERS 



143 



at the front will be higher than at the back when the boiler is being 
forced. If the number of nests or banks of tubes is small, there may- 
be only one upper steam and water-drum. When a number are put in 
one furnace the drums will be two or three in order to secure disengage- 




ment area without inconvenient or dangerous diameter relative to the 
pressure. The long descending elements at the back to each rear header 
are the forces which produce the circulation and keep the active generat- 
ing tubes full of water. If the lower tubes in any bank, from scale or 
oil or inadequacy of water circulation, become hotter and longer than 



144 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




WATER-TUBE BOILERS 



145 



'TL.Li. 





Fig. 145. 



Fig. 146. 




Fig. 147. 



146 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




WATER-TUBE BOILERS 



147 



those above them, a serious cross-stress is brought upon the headers, 
unless the long tubes can flex. These headers were formerly made of 
cast iron, but such unequal expansion was likely to crack any brittle 
material. The gases are made to follow a serpentine course through 




Fig. 149. 



and across the generator tubes, but if the fire is at a high temperature, 
the gases may not be adequately cooled before they leave contact with 
the heating-surfaces. With long-flame fuels it may be desirable to 
build a Dutch-oven furnace in front of the boiler proper, so that the 



148 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

flame shall not be prematurely extinguished by coming too soon in 
contact with the front ends of the cooler tubes. 

In Figs. 148 and 149 the sectional principle is carried still further, in 




Fig. 150. 




Fig. 151. 

that each front header has its own steam and water-drum connected 
also at the back to a common water-drum, and this again to a mud- 
drum. 

The separate steam and water-drums deliver to a common steam- 



WATER-TUBE BOILERS 149 

drum. Furthermore, to reduce the expansion strain the headers are 
not rigid units^ but the end of each tube is connected by a short branch 
with spherical joints at each face to the tube next above it, forcing a 
coil-like circulation until the steam escapes from the upper one in the 
series. Fig. 150 shows details of this construction. 

In Fig. 151 are details of another construction where four tubes only 
are connected and not in the same plane, and with two caps only for 
each four tubes, and these on the inside. Fig. 146 shows the cap 
on the outside. If the holding-bolt breaks from overscrewing, the cap 
blows outward w4th great energy and releases hot water in a four-inch 
stream. Fig. 151 shows an inner plate which will be forced outward 
against the opening if the holding-bolt breaks, and tend to hold back 
the rapid flow of hot water. 

In all these types it has been plain that the fire-room must be large 
enough in front of the boiler or behind it to permit the removal and 
replacement of a tube after service. If the tube is sixteen feet long, at 
least this clearance must be provided within walls. In marine practice 
such long lengths become inconvenient or impossible, and yet wath 
forced draft the necessity of great heating-surface is imposed at the 
same time. This has given rise to forms of boiler using short tubes and 
compactly arranged (Fig. 152). Such boilers are usually set in a 
steel-plate envelope lined with refractory and non-conducting lining in 
blocks. In the form illustrated, the firing is done from the end, but 
it can also have the fire-door on either side, as the construction is sym- 
metrical. Here again, however, the boilers in battery must have 
adequate space to remove any tube and replace it by another. 

It will be obvious that all boilers of the straight-tube type open 
at both ends permit and favor complete inspection from either or both 
ends by placing the eye at one end and a suitable lamp at the other. 
In the water-leg or header type, this means a cap and its joint at each 
end of the tube, and consequent multiplicity of joints and possible 
attendant leakage. Such joints must be ground metal-to-metal joints, 
as no gasket material is appropriate for such a place. If the caps are 
objected to (and with reason), renewal must be by some other expedient 
than from the end; and the cylindrical drum of a size sufficient to be 
entered must replace the flat header or leg. Cleansing by impact 
effected by machine inside the tube is simple and sure in the straight 
design with capped-end openings (Figs. 263 and 264). Fig. 154 
shows the Thorneycroft straight-tube design, depending mainly on the 
absorption of the radiant heat from the fire. 

90. Vertical Curved Open-tube Type. Conceding that the cylindrical 
drum construction for the two open ends of the generating tubes is to 



150 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

be preferred to the header or manifold or water-leg construction, there 
is a limitation to be avoided. Either the bank or nest of tubes must 
include few tubes, or the entry of each tube into the drums must be 
specially molded in the steel to allow the tubes to enter normal to the 




Fig. 152. 



surface of the drum so that a reliable joint can be made by expanding. 
Or, as an alternative design, the tubes must be curved. There is only 
a Hmited surface in the drums presented normal to a common straight 
tube joining them together. If the tube is curved, moreover, expansion 
is provided for in an easy flexure of such tubes in their length without 
straining their joints. Repair or replacement of the inner tubes in the 
nests must still be looked out for, since this cannot usually be done 
from the ends. Fig. 153 shows a type of vertical curved-tube con- 
struction, the gases being compelled to serpentine course by the 
hanging fire-brick brattices or bridge-walls. The tube-sheets are 
made of extra thickness on the drums, and both the lateral steam 
and water-drums deliver into the central one. The lower acts as a mud- 
drum; the coldest descending current is at the back. In the Thorneycroft 
curved-tube type (Fig. 155) this principle is carried to its practicable 
limit, and by the excessive curvature all difficulties are removed 



WATER-TUBE BOILERS 



151 



which would be the consequence of different diameters of the lower 
and upper drums. But this amount of curvature can only be given 
to tubes of comparatively small diameter, leading to the coil or pipe- 




1645- 



FiG. 153. 



boiler. Fig. 156 shows the influence of the Thorneycroft practice in 
yachts and high-speed naval vessels with the curved vertical tube. 

The fundamental objection to the curved tube of more than very 
easy curvature is the impossibility of inspecting it from end to and to 
see what of corrosion or other injury it has undergone in use. Machines 



152 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

for knocking off hard scale by impact with the tube are less easily 
managed. In nearly all vertical tubes, each tube disengages separately; 
and the large water volume at the foot of the tubes keeps them full of 
water. 




Fig. 154. 



FiG; 155. 



91. Horizontal Curved Open-tube Type. American practice has 
not developed the horizontal curved type except for yachts and 
similar conditions. The vertical-tube arrangement, more likely to be 
self-cleansing in good waters, and to a degree even with bad ories, has 




Fig. 156. 



Fig. 157. 



been preferred. In the design of Fig. 157, the tubes are so curved 
as to permit their removal endwise through a side opening of the 
cylindrical drum, which is covered by a proper lid which is long and 
narrow. 

92. Closed Straight Vertical-tube Types. Field Tubes. Another 
direction of trial and design has been to make the generating units 



WATER-TUBE BOILERS 



153 



of tubular or cylindrical elements open at one end only and with no 
joint at the bottom. Such tube will therefore be closed at the bot- 
tom, and will open at its top into the water-drum in which lies 
the disengagement surface. The tube requires to be of sufficient 
diameter that the ascending current of steam-bubbles shall not interfei^e 
with the descending current of water, and this double action seems 
best secured when the tube-unit is inclined about 15° from the vertical. 
Then the bubbles formed in the tube ascend continually along the upper 
elements of the tube, and the lower elements (which are those turned to 




Fig. 168. 



the fire and against which the hot gases impinge) are always bathed 
by the descending water. This was a feature of the Allen boiler 
(Fig. 158), and although it suffered from the difficulty of repair to 
middle tubes, it has been a favorite idea among German designers. 
If, however, the tube is of small diameter, and ebulhtion is too violent or 
the tube too nearly vertical, the steam blows the water out of the tube, 
and it overheats and burns. 

To prevent this trouble and insure circulation in water-tubes which 
have to be of small diameter and essentially vertical, the double tube 
has been used, sometimes called the Field tube (Figs. 6 and 132). 



154 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

Within the exterior and always hotter water-tube proper is placed a 
smaller inner tube concentric with it, kept in place by fins or lugs. 
This inner tube does not extend to the bottom of the outer tube, and is 
open at its bottom. The annular space between the inner and outer 
tube is to be the channel for ascending currents of steam, gas, and water. 
The inner tube will always be full of solid descending water. The 
circulation when the fire is at work should be so rapid and vigorous as 
to wash out and carry up any sediment or scale from the bottom of 
the outer tube where its presence would result in a burning of the tube. 
The circulation is active while the boiler is steaming, but it is not so 
when no steam is being withdrawn, and the circulation is that due to 
convection only. Under these conditions such tubes are apt to fill and 
solidify when least desired. It has been a favorite in fire-engine practice 
(paragraf 75), and has also been used in tug-boat boilers. 

93. Closed Straight Horizontal-tube Types. Belonging also to the 
closed-tube class is a type with horizontal units projecting radially from 
a central vertical shell. The difficulties here are the cleansing of the 
inside of the units, and the indeterminate character of the circulation. 
It has been called the ^' porcupine boiler." 

94. Bent or Curved-tube Types. To avoid the indeterminate cir- 
culation of the closed radial tube, it has been made an open tube by 
bending it back upon itself in an easy sweep, to enter the vertical* water- 
drum at a different level. The difference of level of the two ends is to 
maintain a determinate circulation while steaming, the bubbles rising 
and escaping at the upper end while water enters the lower end to 
supply their place. The tubes cannot be readily cleansed nor inspected 
by eye except for a short distance. The limitations of size for such 
bent or curved tubes put them rather into a class of appendages to 
other types of boilers (paragraf 75 and Fig. 131), and the difficulties 
of repair and maintenance will always keep the design of comparative 
unimportance. The same results are better secured by the pipe or 
coil-boilers of the next chapter and with no greater disadvantages. 



CHAPTER YII. 

COIL AND PIPE-BOILERS. FLASH AND SEMI-FLASH BOILERS. 

95. Introductory. When the demand is for steaming capacity at a 
rapid rate in very small bulk or weight, as in motor vehicles, launches, 
yachts, and small naval vessels, the small diameter of the resulting water- 
tube makes the previous constructions less serviceable. Rapid con- 
tinuous circulation becomes imperative to keep the small tubes clean on 
the inside, since no inspection or access is possible. The tube should be 
of small caliber and the boiler hold little water at one time, so as to 
minimize the disaster if such an uninspected tube fails. Such small 
water-content is also a factor in the rapid steaming. To get length of 
tube or heating-surface in small bulk, the water-tube must be bent back 
over itself so as to form a coil; or a multitude of such partial or complete 
coils united into one generating whole. When the bent tube or pipe is 
formed into more or less helical or spiral coils of some considerable 
length, the boiler will be called a coil-boiler: when multiple partial or 
incomplete coils are connected by pipe-fittings, it will be called a tube- 
and-fittings boiler. The pipe or tube-and-fittings boiler will be discussed 
first. 

96. Tube-and-Fittings Boiler. Fig. 160 will illustrate a simple type 
of tube-and-fittings boiler. The water enters at the bottom and is there 
divided into four coils of tube and return bends. These discharge 
steam and water at A into the annular steam and water-space surround- 
ing the fire and the coil. The heat is radiated from the grate and fire- 
box to make steam also of the water in TT^, and the steam from the coils 
separates from the water as it is withdrawn from the side of the shell 
opposite to the delivery of the coils at A. This boiler is used for fire- 
engine purposes. The pipe and fittings must expand freely within the 
shell; circulation must be rapid enough to keep the coils clean and clear, 
the solid matter from the water going down into the annular separating 
and settling chamber. 

In Figs 161 and 162 are two types of tube-and-fittings yacht or 
torpedo-boat boiler, designed by Almy. Here the separating chamber is 
separate from the generating elements and outside the casing. The 
fire is surrounded by the vertical risers, and each pair of vertical units 
unites into a common riser at the top. The boiler is inclosed in steel 

155 



156 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

with a refractory and non-conducting lining. Certain fittings are 
special, but the manifolds, elbows, and return bends are standard except 
for the way in which the ends of the threads are protected from the heat. 
Each coil-unit, however, is shorter than in the preceding form or in the 
coil-boilers to follow. 




Sectional View, 



Bottom View. 



Fig. 160. 



The curvature of the generating units with elbow and return bends 
takes up expansions; there is very little water in the boiler at one time; 
the subdivision is very thorough. 

97. The Coil-Boiler. The coil-boiler differs from those above men- 
tioned in that one or a limited number of continuous coils is used instead 
of a large number of short or separate circuits. The steam formed near 



COIL AND PIPE-BOILERS 



157 



the bottom end of such a coil must run through its entire length before 
escaping at the disengaging surface. This makes it desirable that the 
water in such a coil-boiler should be circulated mechanically both by 
reason of the advantage so far as efficiency of transfer is concerned, and 
to preserve the coil from burning. Such coil-boilers have given very 




Fig. 161. 



large results for their size in experimental forms. The best-known types 
are identified with the names of Ward, Herreshoff, and Trowbridge. 
Fig. 163 shows the Ward boiler, which has been approved in U. S. Navy 
work of its class, and Fig. 164 is the Herreshoff type. 

98. Sundry Types. Conclusions. There will be types of pipe and coil- 
boilers which will not go naturally into the general classes above named. 
Such would be combinations of accepted types made for special uses 



158 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

and possibly new types. The student and reader must follow his own 
lead in the consideration of such cases. 

It seems to be held in the case of the water-tube marine boilers that 
they present the following features: 

(1) Light weight of both metal and water; about one-half that of a 
Scotch boiler of equal steaming capacity. 

(2) Adapted for high pressures. 




Fig. 162. 



(3) Make steam rapidly, and have the pressure soon after starting 
fires. 

(4) Are safe against a disastrous explosion, because they hold so little 
water. 

(5) Are not injured by the intense combustion and local heat caused 
when forced draft is* used. 

(6) The parts are not difficult to renew. 



COIL AND PIPE-BOILERS 



159 



As disadvantages they offer: 

(7) They require more care in feeding. The water does not always 
remain in the lowest part of the coil and give a normal level at the water- 
gauges. When used in batteries the water may not remain in one par- 
ticular boiler in mass, but will fly about in it or even into other boilers. 




Fig. 163. 



(8) Corrosion is troublesome within the coils, and access and inspec- 
tion impossible. Oil also gives trouble if allowed within the coil with 
the water. 

(9) The coil is prone to fail where the pipes or tubes are threaded into 



160 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



fittings. Overheating from absence of water on the heating-surface 
makes the screw-threaded ends give out by oxidation and by stretching. 

(10) The casing around them gets very hot and makes the fire-room 
or stoke-hold hot even to the point of being unbearable. 

(11) A certain greater amount of air is drawn into the fire around 
the casing so as to dilute the hot gases and lower their temperature. 
This does not occur in a true internally-fired boiler. 

99. Spray Boilers. It occurred to a Mr. Dunbar in the middle of the 
nineteenth century to make steam rapidly by throwing a thin film or 
spray of water upon an intensely heated plate in an inclosed vessel. 
Such water became steam so quickly that it was said to flash into steam. 

The Dunbar boiler failed, however, 
by the deterioration of the plate 
from the high heat and sudden 
changes of form by the impact of the 
cold water. It became coated also 
with the deposits from the water. 
Recently, however, a type of steam 
generator of the coil class has come 
into extensive use for small units 
where great steaming capacity is 
required with small weight* or bulk, 
as in motor-cars and launches. The 
object sought is maximum neces- 
sary heating-surface with minimum 
weight of water in the boiler at any time, the latter both for lightness 
and for safety in case of rupture or failure of any part. The theory is the 
same as underlay the Dunbar spray boiler, which was a generator of 
the shell type, in which at each stroke of the engine there was to be 
injected into the boiler from a feed-pump the same weight of water as 
had just left it in the form of steam for the cylinder. The relatively 
great heating area exposed to fire is so hot that the transfer of heat is 
nearly instantaneous in some forms, and the water seems to " flash " 
into steam-gas. If the boiler contains no water as water for more than a 
fraction of a second, but only wet steam and dry steam, it is a true flash 
boiler; if it contains some water in the process of change, as well as wet 
and dry steam, it is a '' semi-flash" boiler. 

100. Flash and Semi-Flash Boilers. In high-speed engines to be 
supplied from a boiler of this type, the interval required for the heating 
of the water to the boiling-point for the pressure, the heating for the 
change of high-pressure water into high-pressure steam, and the further 
heating for the superheat so easy with this system, have made a necessary 




Fig. 164. 



COIL AND PIPE-BOILERS 161 

gap between the work of a given stroke of the engine and the making of 
steam to supply the volume emptied by such stroke. This fact has 
caused a drift away from the spray or true flash type, and towards the 
semi-flash. In the true flash type the pressure variation is excessive and 
inconvenient when any variation in the load on the engine occurs. 
There is no reserve of heat energy in the form of heated water to bridge 
over the interval of time required for a response to an increased demand 
for steam volume and weight when the latter must be met by an 
increase in the weight of water fed by the pump and an increase in the 
weight of fuel supplied per second to the flame of fire. Such gap in the 
action of the flash boiler is indicated by a sudden drop in the steam- 
pressure as revealed by the gauge on an increase, or an inconvenient rise 
of pressure on a decrease of the demand. In the semi-flash types, where 
some water is always present in the coil, it serves as an accumulator, 
storing heat by reason of its high specific heat for a few seconds as pres- 
sure is rising, and giving this out gradually on a fall of pressure as gener- 
ated steam, and giving time for the controlling devices to diminish the 
injection weight and control the fire temperature on a lessening of load, 
or reverse these processes on an increase of demand for steam as the 
load increases, or the speed of revolution when the latter is variable. 
Plainly, however, the water can have only a limited capacity to act as 
such an accumulator, and when it is exhausted the pressure variation 
will be as in the flash class. 

The leading exponents of these types are the Serpollet (or Gardner- 
SerpoUet) on the continent of Europe, and the White generator in 
America. The Serpollet generator has taken several forms in its develop- 
ment. The earhest was a group of flat spiral coils, made up of flattened 
steel tubing; later, of a series of tubes first pressed so as to bring two 
parallel sides close together (of an inch or J less) and then pressed again, 
so that the section of the opening between the sides was a crescent or 
circular arc for part of the length of each unit. The whole tube was then 
formed into a U, and successive elements coupled together by return 
bends. Later again tubes of cylindrical section were used, or flattened 
tubes twisted; and last of all round tubes formed into a coil of two 
layers, the lower with branches closely parallel, and the upper with 
fewer return bends and at right angles to the axes of the lower. The 
feed-water enters at the top of the series of coils and passes downward 
from the second to the very lowest one, and thence up through several 
(perhaps five), whence it rises outside again to the third and descends 
thence to the outlet. Other foreign forms of this type have been the 
Blaxton generator of England, using plain coils and taking the water in 
at the bottom; the Simpson-Bodman, using dented or Rowe tubes, 



162 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 







•i 




COIL AND PIPE-BOILERS 163 

and types having the unit tubes formed into vertical helices. In the 
White generator the coil is of three-quarter inch steel tube, bent into the 
form of a series of fiat spirals. For a 30 H.P. unit there are usually 
seven of these spirals, aggregating over 320 feet. Feed-water is pumped 
into the coolest coil, which in an upright boiler will be at the top, and 
after passing round the first spiral crosses over the top and descends 
to the next coil below. This method of putting together makes each 
coil a unit, and the inverted U tube which connects it to the next one 
acts as a trap or seal in each case, compelUng the circulation to be 
definite and positive and the separation of steam from water to be 
always at the front or lower end of the moving column. At a point in 
the coil which is variable with the amount of water pumped in as feed, 
the liquid becomes a gas and moves forward over the more intensely 
heated coils close over the fire, toward the outlet at the bottom, becoming 
superheated in its passage, and entering the engine cyhnder in this state. 
The last or final superheating coil being just above the fire at the bottom, 
while the coolest coil is at the top, where the effect of the fire is least, 
secures a graded intensity of the heat transfer, which releases the metal 
of the coils from the great stresses otherwise caused by frequent alter- 
ations of temperature, and secures a long hfe for the coil material, which 
would otherwise be impossible. The intensely rapid circulation makes 
deposit of scale in the coils unlikely, as such separated solids are swept 
forward with the steam and so outward from the generator. The 
superheater coil being in the fire itself, it becomes easy to use the tem- 
perature of the superheated steam as a means to actuate the metallic 
element of a thermostatic pyrometer, the motion of which can be 
utiUzed to open up the water supply when the pressure and temperature 
fall, and to shut off the water supply when the temperature and corre- 
sponding pressure rise too high. Too little water in the generator causes 
excessive superheat, and the fire is at once shut off, so that disaster from 
low water cannot occur. An excess of feed-water, on the other hand, 
will diminish the length of coil acting as superheating surface by increas- 
ing the length which acts to change water into steam. In a generator 
properly designed for its burner or grate area, the effect of this is to 
increase pressure at the expense of temperature, and this pressure can 
be used on a spring-controlled diaphragm to actuate a by-pass on the 
feed-pipe, sending the pump discharge around into the suction and not 
into the generator, and enabhng the latter to void its excess. (See 
paragraf 170.) The advantages attaching to this system arei 

1. The minimum weight and bulk of generator and contents with 
the maximum evaporating capacity possible for a given burner or 
fire. 



164 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

2. Practical automatism of fuel supply and water-feed with simple 
and reliable apparatus. 

3. Prompt response to variation in the demand for steam, without 
inconvenient change in the working pressure on the piston. 

4. Safety from serious disaster: the stored energy at any one time 
is not large. 

5. Scale trouble from bad water is minimized. 

The disadvantages are those which it must share with all curved- 
tube or coil forms as respects inspection, as discussed in the previous 
paragraf. Fig. 165 shows the general arrangement of such a generator 
for motor-car service. 



CHAPTER YIII. 

BOILER FURNACES, CHIMNEYS, AND SETTING. 

105. The Fire as the Source of Energy. It was shown in the analysis 
of paragraf 4 and Figs. 1 and 2 that the steam engine was a heat 
engine. In paragraf 20 the reasons were given for studying the boiler 
before the grate which suppHes heat to the boiler. 

The previous chapters have discussed the heating-surface or absorbing 
area for heat from the fire under or within the boiler, covering the forms 
of such generators and reservoirs of pressure and the accepted designs 
which work well. In this chapter attention will be directed to the 
liberation of that heat energy upon a grate by combustion which the 
fuel is ready to give up. 

Every pound of fuel of constant chemical constitution has a definite 
capacity for heating water. Such capacity is called its calorific power. 
It is either computed from the heating power of its constituents, or 
experimentally determined in a calorimeter.* The latter method is 
more satisfactory. Table IX gives some data upon fuels which may 
be found of convenient reference.* The unit is the pounds of water 
raised one degree Fahrenheit by the complete combustion of one pound 
of the fuel. The weight of 'oxygen required for such combustion is 
found by the chemical formula of atomic combination of carbon with 
oxygen and hydrogen to form carbonic acid and water vapor.* (See 
paragraf 24.) 

To effect this combustion and liberation of heat at the desired rate 
per hour to supply heat to the heating-surface of the boiler and to the 
water which it incloses, the coal must be burned at a rate to deliver that 
quantity. Plainly the leaner the coal, the more must be burned; also, 
the larger the grate the more coal it will receive at one time, and the 
more heat it will deliver with a given combustion rate (paragraf 12). 
The rate of combustion is determined by the draft, or by the supply of 
oxygen or air which is drawn through or over the fire to support such 
combustion. The draft or rate of combustion is caused by the chimney 
or by what may replace it as a force for bringing air to the fuel on the 

* For more complete treatment of fuel calorimeters, calorific power of gases and 
liquid hydrocarbons and the computations for combustion, consult "The Gas 
Engine," by F. R. Hutton. John Wiley & Sons, New York. 

165 



166 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 





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BOILER FURNACES, CHIMNEYS, AND SETTING 167 

grate. (See Analysis, Fig. 2, Nos. 2, 5, and 49.) The grate or furnace 
and the chimney are therefore one unit, designed to effect combustion 
and the Hberation of heat energy from the fuel. What physical and 
mechanical principles underlie the grate and chimney? 

106. Principles underlying the Boiler Grate. The grate must meet 
the following requirements: 

(1) Area sufficient to take at one time the weight or quantity of fuel 
which at the rate of combustion then prevailing will liberate heat 
energy in heat units at the same rate that the engine is using mechanical 
energy in foot-pounds. The steam-gauge is the indicator of this process. 
When the fire energy is in excess, the pressure rises; when the engine 
demand is in excess, the pressure will fall as the energy on storage 
falls. 

(2) Internal resistance in the material of the grate to the stresses 
imposed by the weight of such fuel tending to deflect the grate. Such 
material must not sag or break even when hot. 

(3) Adequate free openings for air to pass into the fire so that the 
chemical reactions with oxygen can occur. As oxygen in air is a gas, 
it can unite only with carbon and hydrogen also as gases and heated to 
a sufficient temperature. When fresh cold fuel is thrown on a fire, 
the first stage is a distillation by heat from the surface of the lumps. 
If this gas meets oxygen and both are hot enough to ignite and combine 
chemically, a flame results and no carbon is wasted. If oxygen is 
lacking, the carbon gas goes off uncombined or partially consumed 
only, and there are unnecessary waste and smoke. If the temperature 
is too low for chemical union, the result is the same as if oxygen had 
been deficient in quantity. 

(4) Resistance to deformation or warping from heat of the fire, and 
of ashes falling hot and burning into an ash-pit below the grate. 

(5) Resistance to mechanical injury from the tools used by the 
firemen in cleansing the fire from clinker and ash. 

(6) It must not be too costly to buy or to replace. 

(7) It must not be heavy to the degree of being unmanageable in 
contracted places. 

107. Principles underlying the Chimney. The oxygen or air to 
oxidize the fuel on the grate will not get there of itself. Some mechan- 
ical energy or force must be expended to bring it there in sufficient 
quantities at sufficient speed and under sufficient pressure to overcome 
the resistances (Fig. 2, Nos. 5, 9, and 49). This force may come from a 
fan or blower driven by expenditure of mechanical power; or the energy 
in heat may be used directly in the construction of the machine called 



168 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



a chimney. The chimney is a device to render available the weight of a 
column of colder air when a definite column of light heated air tries to 
balance it. 

The most widely accepted theory of the action of the chimney was first elaborated 
by Peclet, and developed and quoted by Rankine and other writers. His discussion 
can be made most easily to be understood 
by the conception of the chimney as an in- 
verted siphon, with the fire-grate at the bend 
at the bottom. In Fig. 166 the hatched 
section represents the chimney, and the dotted 
lines the siphon leg of cold external air. 
A diaphragm A-B in the bend of the siphon 
will have unequal pressures on its two sides 
if the legs are of equal length and equal cross 
section, because if Da denote the density of 
the external air and its weight per cubic 
foot, and Dc denote the density of the 
warmer lighter chimney-air, then HDa acts 
on one side, and the less HDc on the other. 
To equahze the pressures an extra effort 
must be exerted on the lighter leg to balance 
the heavier, so that an extra length of column 
of hot air of unknown height h, and having 
a density Dc, must exert a pressure p = hDc 
to effect this balance. Or, since 

HDa = HDc 




+ P, 



Fig. 166. 



we can write 



p = HDa - HDc 



as the pressure exerted on the diaphragm or on a film of air at the base of the siphon 
and which causes the flow when there is no balancing pressure at the top of the 
chimney. But since p = hDc, the height of the column of hot gas will be 



h = 



HjDa - Dc) 
Dc 



and the question of the values of these two densities is a question for observation or 
calculation. At 32° F., D^ for air is .0807, and by reducing Dc to 32° F., the value 
for h can be found in feet, or more conveniently the expression can be transformed to 
read in absolute temperatures instead of densities by the relation that the densities 
will be inversely as the temperatures, so that 

D, Tc • 

But the chimney-gas is a mixture, and not a constant or permanent gas. An 
accepted value for its ordinary density at 32° F. is .08424, which is derived from 
an averaging of many analyses and experiments which give for such gases: 

Carbonic acid 10 per cent, weighing at 32° 12344 

Nitrogen 79 " '' " " 07860 

Oxygen 11 " " " " 08926 



BOILER FURNACES, CHIMNEYS, AND SETTING 169 

Multiplying the per cent of each by its weight, we have: 

Weight of COo. 01234 

" " N 06209 

" " O 00981 

Total 08424 

If the composition of the gases differs from the above assumption as determined 
by analysis or otherwise, additional data are given in the following table: 



Hydrogen 

Oxygen 

Nitrogen 

Carbon dioxide. . 
Carbon monoxide 

Water 

Air 

Ash 



Specific Volumes. 



178.881 
11.2070 
12.7561 
8.10324 
12.81 



12.3900 



Specific Heat in 
Gaseous Condi- 
tion. 



3.4090 
0.2175 
0.2438 
0.2169 
0.2450 
0.4805 
0.2375 
0.2 



Density or Weight 

of One Cubic 

Foot. 



0.00559 
0.08928 
0.07837 
0.12341 
0.07806 



0.08071 



Substituting, then, for D in the formula for height the expression 

Dc = .08424 If, 
^ c 

the expression for that height becomes 



H 



[.0807 ^^-.08424^] 



.08424 J° 

-t C 



which becomes by performing the operations 

;. = //(.96|^-i). 

The velocity in feet per second caused by a height h in feet will be denoted by 
V = \^2gh ; the volume V per second if the cross-section be denoted by A square 
feet will be Av, and becomes 



V^Av^A^j2gH[ ■^'^%-■'^ ) 



for the temperature of 32° F. If it be required to burn W pounds of coal per second, 
and KW cubic feet of gas at 32° F. be the result, we shall have an equation for W, 
since V = KW, 



^^Wf^^(ftfi 



K 

as the theoretical pounds of coal which will be burned by a chimney of height H and 
area A when the resistances to flow of air and gas are disregarded. 



170 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

108. Discussion of Peclet's Tiieory of Ciiimney-Draft. Peclet devel- 
oped a later theory in which the dynamic energy for the flow of air 
to the furnace w^as a head in feet expressed in terms involving the cold 
gas or external air. He also developed an expression for the velocity 
of flow, starting from the general expression for the relation between 
the head in a pipe and the flow which it produces in the case of a liquid. 
A form for this is 



2a V mf 



2g \ 'mi 

which in Peclet's form appears as 



2g \ mj 



In this equation h is the head ; g is the acceleration due to gravity ; / is 

the friction against sides of pipe or duct or flue; K and K^ or G, which 

combines them, are coefficients to express the resistances offered by 

bends, elbows, valves, and fittings in hydraulic work and by the grates, 

tubes, and damper in boiler-furnace work; I is the length of the pipe or 

gas passage; and m is the ratio of area of cross section to the perimeter, 

called the hydraulic mean depth. For square or round flues m^ will be 

¥ b 
one-fourth of the side or diameter, since - — = - for a square flue, and 

46 4 

7rr^ r D 

— = - = ■ — for a round one. Peclet's value for G he puts at 12 for 

27rr 2 4 ^ 

cases where 20 to 24 pounds of coal are burned per hour, and for / his 

value is 0.012 for surfaces covered with soot. Hence his formula 

becomes 



v^ ( 0.012A 

/i= — (13 + ) 

2^ \ ml 



whence the expression for volume per second with a height B. would 
appear 

.96 n- Ta 




13+Mi^ 



m 



The uncertainty as to coefficients; the fact that it is not true that 
V = \/2gh for a flow of a gas which undergoes any notable change in 
pressure or temperature, and the chimney problem introduces both; 



BOILER FURNACES, CHIMNEYS, AND SETTING 171 

the fact that the chimney temperature T^ is not constant from top to 
bottom; and the necessity for the assumptions of area and temperature 
and velocity before a height can be worked out, have thrown designers 
upon the data of experience rather than upon the foregoing calculations. 
♦The Peclet formula, however, possesses this interest. Since the 
velocity of the gas in the chimney increases as the square root of the 
height of the dynamic column, and therefore with \/.96T'^ — T^ when 
the external-air temperature is fixed, and since the density is inversely 
proportional to the temperature in the chimney, the weight discharged 
will be proportional to 

\/.96 T, - T„ 



which becomes a maximum when 

2Ta 25 J 

^^^:%^12^«^^'^^'^' 

or the greatest weight will be discharged when the absolute temperature 
within the stack is f f of the absolute temperature of the external air. 
That is, if the external air be at 62° F., or an absolute temperature 522°, 
the temperature within the chimney for a greatest weight of gas flowing 
should be 522 X If or 1087° absolute, or 626° F. This explains the 
usual preference for temperatures around 600° F. in ordinary boiler- 
stacks. This is about the temperature of melting lead. On the other 
hand, for many metallurgical purposes a higher temperature in the stack 
is a necessity, and a greater velocity than is usual in steam-boiler practice. 
When this maximum temperature prevails h = H; or the extra column 
of hot gas has a height equal to that of the original chimney, and the 
density of that gas is one-half of that of the external air. The formula 
also indicates that chimneys draw best with cold air outside and at high 
barometric pressures. 

109. Some Accepted Chimney Formulae and Data. Mr. WilHam Kent 
in 1884 proposed a formula based on successful practice and on the idea 
that the effective area of a chimney was less than its gross area by a 
dead-space of two inches radially from each wall of a square chimney or 
all around a round one. This idea, if A be the gross area expressed in 
square feet, and E the effective area, will make: 
For square chimneys 

^ = D^ - /2 i) + J- = A - 1 VT. 
For round chimneys 

£J = J (D2 - iV D) = A - 0.592 Vj, 



172 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

This is so nearly the same for both that it can be written 

E = A - 0.6 VA. 

Since the power of a chimney varies both as the square root of its 
height at best temperature conditions and as its effective area, it can 
be written that 

H.P. = EVhx C, 

in which C is a constant to be determined from successful practice. A 
boiler horsepower is assumed to be equivalent to an evaporation of 30 
pounds of water per hour (paragraf 10). Assuming 5 pounds of coal per 
horsepower per hour to take account of poor conditions, and observ- 
ing the number of pounds of coal which a successful chimney will take 
care of, an acceptable value for C is found to be 3J. Hence 

H.P. = 3.33 EVh = 3.33 (A -.qVI) Vh, 



which can be written also 



E 



0.3 H.P. 

Vh 



when the quantities of the second member are the known data. . 

A series of observations by Morin and Tresca from French practice 
have resulted in the following table, which is a very saf-e guide. The 
grate is eight times the chimney cross-section. 



Heights of chimney in feet 

Pounds per hour per sq. ft. grate . . . 
Pounds per hour per sq. ft. chimney 



20 


25 


30 


35 


40 


45 


50 


55 


60 


7.5 


8.5 


9.5 


10.5 


11.6 


12.4 


13.1 


13.8 


14.5 


60 


68 


76 


84 


93 


99 


105 


111 


116 



65 

15.1 

121 



Heights of chimney in feet 

Pounds per hour per sq. ft. grate . . . 
Pounds per hour per sq. ft. chimney 



70 


75 


80 


85 


90 


95 


100 


105 


15.8 


16.4 


16.9 


17.4 


18.0 


18.5 


19.0 


19.5 


126 


131 


135 


139 


144 


148 


152 


156 



110 

20.0 

160 



A simple formula by Thurston agreeing quite closely with the above 
table is 

Rate of combustion = 2\^h — 1, 

in which h is the height in feet. 

Other designers have aimed to deduce formulae from practice which 
should take account of the prevalent resistances in grates and fires with 
different grades of fuel, introducing the results of tests into formulae as 



BOILER FURNACES, CHIMNEYS, AND SETTING 



173 



coefficients. But successful practice of others will remain the preferred 
guiae. Sectional-boiler practice using water-tubes has deduced the 
following diagram (Fig. 167) to represent the draft in inches of water 
corresponding to any number of pounds of air delivered when the 
chimney is luO feet high and the external air is at 60°, as well as the 
maximum readition-point between 500° and 600°. 
Chimneys over 150 feet in height are rarely justified; but 250 feet of 

DIAGRAM OF DRAFT AND CAPACITY OF CHIMNEY, 









kr^^ot 


hv£B" 


t=:^ 





















1 ' 


— 






7=--?^ 


















==- 














-v<o^^" 














-j 


















T^w — 






r-V^tS 


Ur?^ 






















— tA 






.ct \^ 


^^^ 
























/ 




p 


*^^J 


" 
























































































1 
































1 
































/ 
































' 

































































































































Q 00 100 150 SCO 2»0 300 SDO 400 450. &00 &uO COO C50 700 750 800 

Fig. 167. 

height may be compulsory in towns to carry off gaseous or noxious 
products without possibility of nuisance. The following table represents 
conservative data: 



Pounds of coal consumed per hour . . Up to 
Height in feet 



100 
60 



500 1000 
100 120 



2000 
140 



3000 
160 



4000 
180 



5000 
200 



Several smaller chimneys are often used instead of one large one, 
where location does not compel great height, with considerable economy. 

Fine anthracite coal needs a higher stack than good bituminous coal, 
both on account of the grate resistance and the lower temperature of 
the gases, and wood requires less than either of the other two. 

Tallest chimneys on record are: 

Feet. 

Townsend's Chemical Works, Glasgow 468 

Hallsbruckner Hiitte, Saxony 460 

Standard Oil, Bayonne, N. J 365 

Metropolitan Street Railway Company, New York 353 

Omaha & Grant Smelting Company, Denver 352 

Clark Thread Company, Newark, N.J 335 

Manhattan Seventy-fifth Street Station Elevated Railroad (four) 

278 and 17 feet diameter 

Amoskeag Mills, Manchester, N. H, 250 

Narragansett E. L. Company, Providence 238 

Maryland Steel Company, Sparrows Point, Md 225 

Passaic Print Works, Passaic, N. J 200 

Edison Electric Light Company, Brooklyn (two) 150 



]74 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

110. Dilution of the Products of Combustion. In the burning of 
solid fuel involving the two stages of distillation and subsequent chemical 
union, the latter step takes place reluctantly in an atmosphere charged 
with carbonic acid, which is not a supporter of combustion. Hence the 
chimney and the draft arrangements of the grate must be planned to 
give from one and one-half to twice the air supply which is theoretically 
required. This extra weight of air carrying inert nitrogen makes 
demand on temperature of the fire to heat it up, or in effect cools the 
fire» 

In burning gas or liquid fuel made by spraying into a mist of atomized 
particles, no such excess of air is required, and this is one cause of the 
superior effectiveness of such fires. If the air can be preheated by 
otherwise wasted heat, considerable saving results. 

111. The Grate-Bars. Stationary Grates. The problems which the 
boiler grate must meet (paragraf 106) have been solved by making 
the grate of bars, either of cast iron or of wrought iron, solid or hollow. 
Grate-bars may be divided into three classes: the fixed or stationary 
grates, shaking and dumping grates, and mechanical or traveling grates. 

The stationary cr fixed grates are almost always of cast-iron bars 
(Fig« 168). It is most usual to run these bars lengthwise or in the 
direction of the axis of the boiler and perpendicular to the front. It is 
easier to clean them when arranged this way. They will be supported 
by transverse bars, usually of wrought iron, let into the brickwork of 
the side walls (Fig. 169). There is usually one at the front and one 
at the back supporting the bars at their ends. It may be, however, 
that instead of running the bar continuously the- whole depth of the 
furnace, it will be divided in the middle, and each short bar will rest 
upon a third bearer midway between the other two (Fig. 189). 

It would appear that a maximum relation between the supporting 
function of the bar and free passage of air would be reached when each 
was made 50 per cent of the surface of the grate. Practically this 
relation cannot be reached without causing much unburned fuel to fall 
into the ash-pit to be wasted, or to entail the labor of picking over if it is 
to be saved. The difficulty is worse as the size of the fuel grows smaller. 
It is usual to consider the bar satisfactory for the passage of air when 
25 per cent of air-space is presented by its design. The proportion of 
air-space to solid surface of the bar is usually determined by the 
expedient of laying the bar upon a piece of stiff paper, tracing its profiles 
of openings with a sharp pencil, cutting out the paper representing the 
openings, and weighing on delicate scales the relation of the weight of 
the air-space and soHd bar in any given unit of area. 

The usual deterioration and failure of grate-bars come from their 



BOILER FURNACES, CHIMNEYS, AND SETTING 



175 



warping, from fusion of the top surface, and consequent softening and 
loss of strength, and from breaking through by their own deterioration or 
from a deterioration caused by the continued heat. 





^ --^i 




Fig. 168. 



Wrought-iron bars when made sohd are particularly troublesome from 
a tendency to warp and to bend from softening by heat. Wrought iron 
is less stiff than cast iron. 

When for any reason the air which enters under the grates is to be 
preheated so as to lose its cooling effect, solid grate-bars of either cast or 
wrought iron give trouble by their softening. For this condition and in 



176 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




Fig. 169. 



certain other places hollow wrought-iron grate-bars are used through 
which the feed-water or the water from the boiler is caused to circulate. 
This is to keep them from reaching the temperature of softening, and 

adds to the heating-surface of the boiler. 
The difficulties from the expansion of 
such water-grates make them trouble- 
some to join to the ends, but they have 
formed a satisfactory solution for many 
problems, and are a necessity in what is 
called the down-draft furnace (Fig. 202), 
to be referred to hereafter. Some of the 
bars in locomotive-boilers are usually 
water-tubes. 

With very fine fuel, such as coal-dust, 
and where sawdust is used as fuel, the 
grate-bar has to become a perforated 
hollow tube or a plate (Fig. 173). 
Where oil or gas is used the grate-bar 
disappears entirely, and the gas will be 
passed up through the perforations made in a fire-brick or similar floor 
which converts the grate into a form of burner. 

112. Shaking and Dumping Grate-Bars. The stationary or fixed 
grate-bar is cleaned by running a proper tool, called a slice-bar, over 
the top surface, or a poker between the bars. This is a labor of con- 
siderable difficulty and requires that the furnace-door should be open 
while it is going on, and the cold air thus admitted not only deadens 
the fire but cools the heating-surface and checks the generation of 
steam. What are called shaking-grates are grates whose bars are so 
constructed that by a lever or similar means a motion can be given to 
the bars, from without the setting, whereby the fire shall be agitated, 
the fine dust or ashes shall be shaken downwards through the openings 
of the bars, and the ash or clinker which has attached itself to the top 
surface of the bars shall be broken up and ground into pieces fine enough 
to drop through and leave the fire clean. This result is attained in 
various designs of grate-bars by different mechanical methods. In 
some the bars are supported by proper bearers at their ends, to which 
bearers such a motion is given that the alternate bars move lengthwise 
in opposite directions through several inches of travel when the lever 
of the shaking mechanism is worked (Fig. 170). In others each individ- 
ual bar receives a rocking motion around the axis upon which it is 
supported. The rocking motion lifts the fire and lowers it, thus shaking 
out the accumulation of ashes and dirt. 



BOILER FURNACES, CHIMNEYS, AND SETTING 



177 



Dumping-grates are a form of shaking-grate in which the motion 
which shakes the bars when carried farther opens sufficient space 
between the adjacent bars to allow the fire to sHp off the top surface 




Fig. 170. 




Fig. 171. 



of the bar into the space thus opened and fall into the ash-pit below. 
The difficulty with the dumping type of grate-bar is that carelessness 
in its use causes a loss of an excess of fuel in cleaning (Fig. 171). 




178 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

Fig. 172 shows a design in which the throwing of the bar from the 
level position of service to the front gives the shaking motion, and the 
lifting of the front of each bar or its throw to the back gives the 
dumping effect. In Fig. 173 the bar proper is hollow with air openings 




FiQ. 172. 

on the upper surface and is intended to operate with forced draft. The 
bars are rocked by a side-to-side motion across the front of the boiler. 
The advantages of the shaking-grate are as follows: 
(1) The fire-door is opened for coahng, but not for cleaning.. 




Fig. 173. 



(2) The fire-box lasts longer, because not exposed to the shrinkage 
and deterioration caused by cold air coming in upon its heated surface. 

(3) The firing is more regular, because the fires are kept in a condition 
of good efficiency by being always clean, and are not torn to pieces by 
the effort of the fireman to cleanse them. This is particularly true with 



BOILER FURNACES, CHIMNEYS, AND SETTING 179 

anthracite as a fuel. One man can attend to more furnaces when the 
labor of attending to each is so much lightened. 

(4) The duty of the fireman is made less arduous and exhausting 
when he does not have to face the intense heat of the furnaces at the 
open doors for so long a time. 

The objections to the shaking-grate are as follows: 

(1) It does not work with all varieties of bituminous fuel. Where 
the coal is what is called fat, so that it fuses together on the upper 
surface of the fire, the shaking-grate does not cleanse the fire, but only 
leaves a hollow space below the real body of the fire. For coal of this 
class the use of the slice-bar is necessary in any case, and it might as well 
be used altogether. 

(2) The trouble and annoyance from machinery of any sort in an ash- 
pit. It cannot be lubricated; it is exposed to grit and dust. 

(3) The efficiency of the bar for cleansing usually throws down 
excess of linburned fuel into the ash-pit. The shaking-grate for station- 
ary practice is usually considered to be a stepping-stone on the way to 
the use of mechanical stoking, and its advantages are usually reaped 
with the advantages which the latter offers. 

113. Step-Grates. For the burning of fine coal, and particularly in 
soft varieties where a large quantity of air is a necessity, a form of grate 
has been long used which is called the step-grate. The bars are flat 
surfaces or treads arranged so that the upper one slightly overlaps the 
one below it, while leaving the space open which corresponds to the 
riser in stairway construction for the passage of air. It will be seen that 
this construction permits abundance of access of air with little or no 
possibility of coal dropping through the grate-surface. When the bars 
are laid across the furnace, as is usual, the slice-bar of the fireman can 
cleanse each bar separately by working through the vertical opening 
between the bars, or the method of firing may be used whereby the coal 
is fed first on the upper bar, and from that is gradually pushed down the 
steps from bar to bar until at the bottom it will be pushed off with all 
available combustible matter utilized, and only refuse and ash remaining. 

It is very easy to make such a step-grate become a shaking or 
dumping-grate by arranging each bar so as to permit a motion to tip 
it down the steps. This can be done either by hand or by mechanical 
means (Fig. 174). 

114. Mechanical or Traveling Grates. — The principle of successive 
passage of fuel from bar to bar suggested in the previous paragraf 
leads to a construction of grate which is known as the traveling-grate. 
The bars, instead of being continuous and soUd, are made up of a series 
of short bars which are pinned together so as to form a flat chain with 



180 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




BOILER FURNACES, CHIMNEYS, AND SETTING 



181 



the links edgewise. Chains of these flat Unks, made endless, mounted 
upon proper carrying-rollers at the front of the furnace and at the rear, 
and having the width of the furnace area, can be driven by machinery 
attached to the rollers so as to draw the chain from the front of the 
furnace to the back, carrying on its surface the fuel to be burned. 
The speed of driving should be so proportioned that the fresh fuel 
charged at the front upon the traveling-bed of the grate should l)e 




^«»■..^^_^^_ --.-_-77r:rr-;:^=L-cs.v:^-.>^-^il'l-'-lJt---J.--0---^^ 1_ 



Fig. 175. 



completely burned during the period of its transition to the back, 
so that when a given series of links reaches the rear roller and is dropped 
over, there is carried mth it and dropped only the incombustible 
matter in that given amount of coal. Such a grate is practically self- 
cleansing and leads at once to the use of an automatic appliance for 
feeding the fuel to it to make it complete. Fig. 175 w^ill show a typical 
traveling-grate, and Fig. 174 a type of grate in w^hich the passage of 
fuel from step to step is made to be automatic by mechanical means. 
It will be seen that the mechanical grates of this type lend themselves 
and lead naturally to the principle of the automatic stokers. 

115. Mechanical Stokers. A combination of a mechanical grate 
with a mechanical feed of the fuel constitutes a mechanical stoker. 
This is aimed to secure both economy of labor and complete and eco- 
nomical combustion. Inasmuch as the mechanical feeding is an aux- 
ihary equipment of the power plant, the discussion of the stoker will 
be postponed till the discussion of such auxiliaries is taken up . in 
Chapter XIII, as paragraf 223. 

116. Inclined and Horizontal Grates. It will be noticed by examining 
Figs. 178 and 179 that a difference of practice prevails with respect to 



182 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

arranging the grate-bars horizontally, or inclining them downwards at 
the back in the proportion of about 3 inches in 6 feet. The practice of 
incHning is quite usual, in order that the under surface of the fire may^ 
come more nearly normal to the incoming air-currents, so as to invite 




them to pass equally through all parts of the fire, rather than to take 
the easiest course. In sectional boilers with inclined water-tubes the 
inclined grate is of advantage in keeping the surface of the radiating 
fire more nearly parallel to the absorbing surface of the tubes. Inclined 
grates are also easier to clean by slicing. 

The horizontal grate renders it more easy to keep the fire of even 



BOILER FURNACES, CHIMNEYS, AND SETTING 



183 



thickness at the front and back, and makes it slightly easier to withdraw 
the clinker and other solid matter which is to be drawn forward and 
out through the fire-door in arrangements of this sort. The general 
prevalence of the inclined bar seems to indicate that it offers advantages 
over'the other arrangement. 

The level of the grate-bars with hand-firing should be so selected as 
to make the cleaning and coaling convenient to the fireman. This 
seems to be secured by having the top of the grates from 24 to 30 inches 



11 S15 Manhole 




Fig. 179. 



above the general floor-level. The depth of the furnace or the length 
of the bar with hand-firing seems to be determined by the twofold con- 
siderations of ease of cleaning and the satisfactory spreading of fuel. 
When the fireman stands on the floor-level he can easily deliver coal 
with precision at the back of the grate, which is 6 or even 7 feet deep. 
When he stands above the grates, as in the case of the locomotive, 
he can throw coal to the back of a fire-box 10 feet deep. Cleaning, 
however, by hand, cannot easily be done with a furnace deeper than 
6 feet, and this is usually placed for the limit of the length of the grate- 



184 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



bar. With shaking or mechanical grates the grate could be deeper if 
it were otherwise desirable. 

117. The Firing on the Grates. There are two systems to realize the 
complete double stage process of combustion with solid fuel. The one 
is called the side-firing system and is easily carried out when the furnace 
is wide enough to require two doors for complete access for firing and 
repairs. In this, the furnace is supposed to be in two halves lengthwise, 
and each half is fired alternately with respect to the other. The coal is 
thrown, for example, on the right-hand half through the right door at the 
time when the left-hand half has completed the distillation from the 
black fuel, and all that part is in red glow and full combustion. In 
side view, therefore, it looks Hke Fig. 180. Then when the right half is 
all aglow and no more smoky-looking gas is coming off, the left hand 





Fig. 180. 



Fig. 181. 



receives fresh coal, and so on. In the other or coking system, the fresh 
coal is always thrown on the dead area in front of the grate-bars 
(Fig. 182) and when warmed enough is pushed back on the front end 
of the bars (Fig. 181) where distillation is active, and the gases minghng 
with the hot flame and products of complete combustion are made hot 
enough to burn also. When distillation is complete the incandescent 
fuel is pushed back and fresh coal charged at the front. The fire should 
be of uniform thickness on the grate to give uniform distribution of 
oxygen, and there should be no holes in it to allow cool air to break 
through without supporting combustion. Such jets of cool air stop 
generation of steam and are bad for the shell. 

118. The Dead Plate and Furnace Mouthpiece. The front end of the 
grate-bars should not project beyond the end of the heating-surface of 
the boiler, and therefore a distance equal to the depth of the smoke- 
box will lie behind the fire-door and between it and the end of the bars. 
This gives a width of space which serves as a dead-plate for the coking 
method of firing when it is desired to adopt it, but even with anthracite 
firing, where no coking is required, the dead-plate remains as a distance- 



BOILER FURNACES, CHIMNEYS, AND SETTING 



185 



piece, but without significance or use in firing. It usually forms the top 
of the opening into the ash-pit below, and is simply a plate of cast iron 
built into the brickwork of the setting at the sides (Fig. 182). In some 
cases the dead-plate has been made to drop by hinging the front end 




Fig. 182. 

against the boiler-front and holding up the back by a latch which can 
be released. The object of this arrangement was to permit clinker 
and ashes too large to pass through the grates into the ash-pit to be 
dumped into the latter over the ends of the bars without coming out 
through the fire-door and causing unpleasant odors from any cause which 
such material might give off in the open fire-room. 

The sides and top of the furnace-mouth opening will be made either 
of cast iron, like the dead-plate which forms its bottom, or of fire-brick. 
The latter may be either the ordinary forms of fire-brick, or specially 
molded shapes can be obtained whereby the mouthpiece has but a 



186 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

few joints in it to give trouble in service. The mouthpiece must flare 
towards the furnace in order that an opening smaller than the width 
of the grates may permit access to every part of the grate, and the 
injury from firing-tools and from the action of the heat of the fire makes 
trouble with ordinary brick construction. The arch over the door is 
also a flat one which it is troublesome to make and maintain if of many 
separate pieces. The sides are sometimes of the usual sizes of brick, 
and the top of cast iron. 

119. The Ash-Pit. The ash-pit, as its name indicates, is to catch 
the refuse incombustible matter when the fires are cleansed. It is 
simply formed by the sides which form the furnace, and is paved on its 
bottom with fire-brick also. The bottom is sometimes made lower 
than the general floor-level (Fig. 183) in order that water may be 
allowed to he in the depression thus formed. The object of the water 




Fig. 183. 



is first to quench incandescent matter which if allowed to glow in the 
ash-pit would heat and soften the grate-bars. It is desirable also that 
if sulphur-gases are given off from such ash, the process should be stopped 
at once. It is further urged that the steam formed from this water 
will tend to keep the grate-bars cool on its passage through them, and 
the combustion of the hydrogen, when such steam is dissociated in the 
fire, will add to the heat of the usual combustion. The objection to 
this is that the dissociation of the steam cools the fire itself exactly to 
the same extent that the combustion of hydrogen would raise its tem- 
perature. With short-flame fuel the hydrogen may act to lengthen 
the flame and increase the effect of radiation in a perceptible degree. 



BOILER FURNACES, CHIMNEYS, AND SETTING 



187 



With long-flame fuel its effect is not observable. It is a question 
whether steam from the ash-pit may not act to rust metallic surfaces 
and to form a more active compound with the sulphur-gas given off 
than when that gas is dry. 

When the air for combustion is to be supplied to the fire by mechanical 
means so as to create an artificial draft by pressure below the grates 
(paragrafs 126-128), the flues or ducts for such artificial draft will 
be carried into the ash-pit. The best places are the side walls, rather 
than the bottom, since it is difficult to keep ashes from dropping into 
the ducts when the openings are directly under the grates (Fig. 201). 
These openings will be controlled 
with proper dampers operated from 
outside of the setting. 

In large plants where the weight 
of ashes to be disposed of in any 
day becomes very large, it is worth 
while to arrange the ash-pits so as 
to deliver their accumulations into 
a tunnel underneath them through 
which a suitable wagon may be 
wheeled to receive the contents of 
each pit as it stands under a 
convenient opening below it. This 
principle also becomes of impor- 
tance when the mechanical methods 
of firing are used whereby the grate 
is made to be self-cleansing and 
discharges its ash and incombus- 
tible matter continuously over its 
end. If the wagon method is 
inconvenient, it may be replaced 
by a continuous conveyor whereby 
the discharge from each grate or 

ash-pit falls upon a continuously moving band, and is carried by it and 
dumped into some convenient receptacle outside. 

120. The Bridge-Wall. — The back of the ash-pit and of the furnace 
or fire-box is made by a low wall over whose top the gases and products 
of combustion are to pass. It separates this space in the setting from 
the combustion-chamber behind it. In so far as it is merely a 
separating wall it might be made of 8 inches in thickness, but inasmuch 
as with stationary grates it is liable to suffer impact from the slice-bar 
in cleaning the top of the grates, it is more usual to give it a thickness 




Fig. 184. 



188 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



from the bottom to the line of the grates of 2^ or even 3 bricks length- 
mse, giving a dimension of from 20 to 24 inches. It is not necessary 
that at the top it should be of this full width, and therefore it is quite 




usual to taper it from the line of the grates backwards, either from the 
front or from the back, so as to give it a width of one brick or 8 in<;hes 
only at the top. Examples of both methods of tapering will be found 
in the illustrations Figs. 178 to 188. The objection to tapering from 



I 



BOILER FURNACES, CHIMNEYS, AND SETTING 



189 



the front or fire-box side is that so much of the fire as Ues upon the 
sloping surface does not receive its full proportion of air, although this 
is corrected in part by the slanting direction which the air takes in 
passing from the grates to the top of the bridge. The diminished 
thickness at the top is of advantage in diminishing the friction of the 




gases in passing over the bridge, and in rendering it unlikely that 
misdirected fuel will be caught upon it. It will be observed also that 
there is difference of practice as to making the top of the bridge-wall 
a horizontal line, or an inverted arch parallel to the circumference 
of the shell. The inverted arch is supposed to direct the currents of 



190 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

hot gas and flame close to the shell. It makes, however, a very deep 
corner where the height from the grate-surface is much greater than 
at the middle. The horizontal wall is easier to make, keeps the fire 
of equal intensity over its whole width, and the tendency of hot gas 
and flame is to keep to the upper part of its passage in any event. 

The bridge-wall is represented as sohd in the foregoing illustrations: 
it is quite common to perforate its rear at or near its top, and to make 




Fig. 187. 



openings into a hollow within it to which air can have access from 
the outside. The outside of the setting will force air in through this 
hollow wall, where it will become heated by contact with the hot 
bricks, and passing through the opening will mix with the flowing 
products of combustion over the top, and help to complete their com- 
bustion (Fig. 188). With this same purpose the bridge-wall is often 
made of a hollow cast-iron box Avith similar perforations at its back. 
It will be seen also that a metallic bridge-wall may be filled with water 
to be evaporated, and, if proper circulation is kept up within it, it can 
form an efficient addition to the heating-surface. If water-grates are 
to be used in a brick setting, the water bridge-wall becomes, practically, 
a necessity. 

121. The Combustion-chamber. — Behind the bridge-wall and under- 
neath the shell of the boiler is an open space intended to permit 
complete combustion of the carbon which may come over the bridge- 
wall in the form of flame or combustible gas. For this reason it is 
called the combustion-chamber, even if, as is the case in anthracite 
practice, there is really no combustion to take place within it. It is 
desirable to have it with gas-fuels in order that a space may be made 



BOILER FURNACES, CHIMNEYS, AND SETTING 191 

in which the boiler shall not be too closely forced into contact with the 
hot gases and extinguish them by its lowered temperature, and, further- 
more, in which there shall be permitted both room enough and time 
enough for a proper union of oxygen with the gases. It is furthermore 
of advantage, if otherwise practicable, to introduce refractory bricks 
or similar material into this combustion-chamber which shall serve 
to keep up the temperature of the flame and gases above the point 
below which no chemical union can occur. In anthracite practice this 
chamber can be filled up in part or largely without disadvantage. 
In bituminous practice this would cause a smoky and wasteful com- 
bustion. Fig. 189 shows a type of a setting prevalent at one time in 
which the small size of the combustion-chamber may be credited with 
causing very smoky chimneys. The combustion-chamber serves also 
as a catch-chamber to hold some of the particles of ash and flue-dust 
which will be drawn out of the fire by a strong draft, but which will 
be precipitated by the lower velocity of the gas-currents in the large 
area behind the bridge-wall. This makes it necessary that there should 
be doors of access into the combustion-chamber, that it may be cleaned 
out at intervals, and such doors give also a convenient access for inspec- 
tion of that part of the boiler. These doors will usually be of some size 
(perhaps 18 or 24 inches wide by 18, 24, or 36 inches high), and they 
will be made by buildiflg a flanged framework of cast iron into the 
brickwork which will clasp the flange, and be supported by them 
while the projecting plane beyond the brickwork carries the hinges 
(see H in Fig. 182). The door-openings are objectionable, because 
they break the continuity of the brick wall and cracks originate from 
them for this reason. It would be desirable not to put them at the 
bottom on account of this tendency to create cracks, which are less 
troublesome if they are towards the top. The location of the doors in 
the side or back wall of the combustion-chamber must be a matter 
of convenience and location, but the back wall is not as good a 
place as the sides by reason of the effect of direct impact of flame and 
gases. 

In sectional-boiler settings the combustion-chamber is partly filled 
by the boiler itself, or rather it is made from a space within which are 
the tubes. The absence of return fire-tubes in boilers of this class 
compels the gases to receive a circuitous path in and out among the 
water-tubes, and this is secured by partitions of fire-brick like hanging 
bridge-walls, which force the gases to pass around them and meet 
complete combustion while still in contact with the tubes. It is prob- 
able that the gases will be hotter when leaving a sectional boiler than 
in leaving a return tubular boiler for these reasons. 



BOILER FURNACES, CHIMNEYS, AND SETTING 193 




G 



d 



Q 



G 



tn 





194 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

122. The Back Connection. — The hot gases passing backwards 
underneath the shell of the boiler are to be deflected into the tubes or 
flues in order to come forward through them to the front. Following 
the analogy of the internally-fired boilers, this space at the back end 
of the setting in which the tube sheet comes has been called the back 




Fig. 190. 

connection. It is apt to be about 2 feet deep, and must be 
roofed at the top at such a level that the flame and hot gases impinging 
against the back head shall not heat the surface of that head, which 
is not protected from overheating by water on the inside. It will be 
seen from examination of Figs. 178 to 214 that there are three methods 
for making this roof of the brick connection. 




Fig. 191. 



First, the roof may be made of an arch whose axis is transverse to 
the setting, and of which the boiler itself shall form the keystone and 
take the thrust of the arch (Fig. 751). 

In Fig. 191 is shown the scheme of hanging this semi-arch from a 
bearer resting on the side walls, taking off the thrust on the boiler 
and giving longer life to the arch. 



BOILER FURNACES, CHIMNEYS, AND SETTING 195 

Second, the roof may be flat, the bricks which form it being supported 
upon transverse bars of cast or wrought iron which rest upon the side 
walls and support the bricks. Cast iron is better than wrought from 
its resistance to softening by heat, and the usual shape is a T iron with 
its cross downwards and the web of the T among and between the 
bricks (Figs. 178, 188). 

The third plan is to arch the roof with an axis parallel to that of the 
boiler and with its abutments on the side walls. The fire-brick is 
supported as in the second plan by a cast-iron arch bar ribbed on its 
upper side for stiffness (Fig. 190) so that its section is T-shaped in the 
middle. Without the bars arch would deteriorate by heat and fall in. 

If the first method is used, the back end of the boiler must be the 
fixed end, and expansion be from this end towards the front. The 
back connection must be large enough to give convenient access to the 
back head of the boiler for any repairs which may be called for at that 
point. 

133. The Front Connection. The gases which pass through the flues 
or tubes are to be gathered together at the front head and discharged 
into the stack. When the front end is not made a smoke-box it will be 
called the front connection. The gases should have parted with a great 
deal of their heat in passing through the flues or tubes, so that their 
volume is less, and for this reason the front connection is usually about 
two-thirds the depth of the back connection. Sectional boilers have no 
front connection, but the gases pass directly from the back connection 
to the stack. The front connection gives access to the front head of 
the boiler, and the flue-doors of the boiler-front admit to it from the 
outside. 

134. The Flue to the Chunney-Stack. When the front connection is a 
smoke-box in extended front settings, and in many cases of full front 
settings, the gases pass directly through an opening into a metaUic flue 
which carries the products of combustion to the chimney and so to waste. 
If there are several boilers side by side or in a battery, short lengths 
of flue from each front connection or smoke-box will unite them to a 
larger flue increasing in size as additional quantities of gas are discharged 
into it, and through this common flue they pass into the chimney 
(Fig. 192). 

When the chimney is at the back of the setting a customary arrange- 
ment has been to carry the gases to the rear in a flue formed by spring- 
ing an arch over the top of the boiler from side wall to side wall. The 
tie-rods and buckstays withstand the thrust of this arch, and from the 
space thus formed the gases pass to the chimney. Figs. 75, 168, and 
193 show this arrangement clearly. 



196 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

It offers the following advantages : 

(1) Radiation is diminished from the top and the boiler is kept warm 
by its own gases. 

(2) If these gases are hot enough, they have a tendency to dry or 
even shghtly to superheat the steam in the steam-space and in the dome. 

The objections to this construction are: 

(3) It is of small value as a superheating appliance, because shortly 
after starting the boiler is thoroughly covered with a coating of fine 
ashes or dust which is practically a non-conductor. 

(4) It is difficult and usually unwarrantedly expensive to construct 
the opening through which the dome of the boiler must protrude, and 
the expansion of the boiler in the brickwork opens cracks for leakage of 
air into the flue. 




Fig. 192. 



When, however, the chimney must of necessity be at the rear of the 
setting of such boilers, these difficulties can be avoided suflftciently 
well to make it a justifiable feature of settings for anthracite coal, but 
not for bituminous. It should be large enough to permit the access of a 
man for inspection. 

Where it is not used, the top of the boiler will be covered with some 
non-conducting material laid on in sections which shall permit their 
removal for inspection. These non-conducting coverings catch and hold 
any water of leakage, and unless care is taken may occasion external 
corrosion. 

125. The Damper and Damper-Regulator. In order to control the 
action of the chimney, which depends on the weight of a column of air 
outside of it, a valve of some sort is required in the flue from the boiler. 



BOILER FURNACES, CHIMNEYS, AND SETTING 



197 



When closed wholly or in part it causes a friction in the discharge of the 
gases through it, which checks the flow of air through the fire. 

It is usually made in one of two forms. The sliding or guillotine 
damper is a flat plate sliding in grooves across a frame in the flue 
(Fig.' 75). The pivoted or balanced damper is a plate mounted upon 
an axis through its center of gravity by which it can be turned so as to 




stand edgewise to the flow" of gas, opposing little resistance, or flatwise 
to it so as to close the opening altogether. The sliding damper usually 
is the harder to move, 'and if it slides vertically has to be counter- 
weighted in order to be balanced. The other form is in equilibrium in 
any position. The damper is often arranged not to close entirely even 
when it is nominally shut, in order that there may still be a tendency 
for a current to be maintained inwards through the setting, and out 
through the stack to prevent undesired gases from getting into the boiler- 
room because access to the chimney is closed. 

Since the chimney is the immediate and usual method of controlling 



198 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

the fire, it becomes exceedingly simple to make it automatic, so that the 
fire shall be somewhat self-regulating. The pressure of steam can be 
brought against a piston, and the motion caused by that pressure can 
be resisted by a weight or spring. When the pressure exceeds the normal, 
the weight will be overcome; when it falls below the normal, the fall of 
the weight will move the piston the other way. The motion of the 
piston, which can also be made a diaphragm of flexible metal, can be 




Fig. 194. 



attached to the damper so as to close or open it when the pressure rises 
or falls. This may be done either directly, as in some of the older forms 
of damper-regulation (Fig. 194), or the steam-pressure may move a 
valve to admit the pressure which operates the damper, upon one 
side or another, of the mechanism which moves the latter (Fig. 195). 
This may be the water-pressure of the city mains, or it may be the 
pressure from the boiler of the steam or water in the boiler itself. 

126. The Chimney. The effect of height in the chimney as causing 
flow of cold air into the ash-pit has been discussed in paragrafs 107— 
109. The weight of chimney-gas moving per second through the fire 
is conditioned both upon velocity and cross-section: and these vary 



BOILER FURNACES, CHIMNEYS, AND SETTING 



199 



inversely as each other for a fixed weight of gas. Too large a cross- 
section makes the chimney draw badly because the lower velocities cause 
eddies and back-draft: the chimney is unnecessarily costly to build; 
and the gases are unnecessarily cooled by contact with the large 
chimney surface. Hence the standard cross-section exists of one- 
eighth the grate area as representing successful relations between grate 




Fig. 195. 



area and chimney area. This can be shown to be ample for any 
normal velocity, for if an area of one square foot be taken, and a 
temperature for maximum output v^ = V2gH, and if H be taken at 
64 feet of height for illustration, 

v^ = 64 cubic feet per second 

- 64 X 3600 = 230,000 cubic feet per hour. 



200 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

Suppose 20 pounds of coal burned per hour per square foot of grate, 
and 300 cubic feet of air per pound of coal ; then 20 X 300 = 6000 cubic 
feet of air at 62° will be required per square foot of grate. At 626° F. 
in the chimney this air will have twice its volume at 62", since 



v^ = y„^=6ooo^-«'«'* 



arr, -"— 5^T > 



whence 

V, = 12,500 cubic feet, 

which, if multiplied by the assumed relation of chimney 1 : grate 8 = 
96,000, is only about ^5^^o°o%7 oi* one^third of what the chimney of only 
64 feet high will take care of per foot of area of cross-section. 

The friction becomes greater if the chimney be too small, and plants 
are usually enlarged after some years of use. Hence, although this 
one-eighth value is large, it is usually best not to pass much below it in 
small plants. Possible excess of area is corrected by partly closing the 
damper in the flue to the stack. 

An ingenious designer has proposed to use the dead area of the Kent 
formula, or the back-draft area in the above discussion, as a passage to 
bring preheated air down the stack so as to introduce it above the fire 
and avoid the consumption of fuel required to raise this air to fire- 
temperature. 

The chimney foundation problem belongs rather to structural engi- 
neering than to a treatise upon power, and it would divert from present 
purposes to discuss these questions at length. Wind-pressure is not 
likely to reach 55 pounds per square foot of flat surface; and the chimney 
may be viewed as a cantilever loaded uniformly with this load. In 
brick structures this must never produce tension on the windward 
side, when compounded with the resistant weight of the bricks, which 
will range from 100 to 130 pounds per cubic foot; nor on the compres- 
sion side must the stress exceed 8 tons to the square foot, which the brick 
should be able easily to withstand. That is, if h be the height in feet, 
d the average breadth, and h the breadth at the base, there must be 
equilibrium between W, the weight of the chimney in pounds, and the 

quantity C —— . In the latter, the coefficient C is a factor for wind- 
pressure per square foot of area. It is 56 for a square chimney, 35 for an 
octagonal, and 28 for a round chimney. A brick chimney so propor- 
tioned will withstand any gale Ukely to be experienced. It will appear, 
however, that a chimney from these causes and the concentration of 
weight on a small area is a structure particularly liable to unequal 



BOILER FURNACES, CHIMNEYS, AND SETTING 201 

settling of its foundations. The latter, therefore, should receive most 
careful attention from a competent designer of foundations, and should 
be laid by experienced persons. Natural and undisturbed soil will carry 
one ton per square foot; loam, compact sand, or hard-pan can carry two 
tons per square foot. Where natural foundations cannot be had, piling 
and other artificial methods are to be resorted to. 

With respect to their structure, chimneys may be grouped into 

(1) Brick. 

(2) Steel or iron shell, brick-lined. 

(3) Skeleton iron and brick. 

Brick chimneys are round, square, octagon, or star-shaped. Circular 
section seems best, as lighter, stronger, and more shapely. English rule 
is, base equals one-tenth of height; the batter or taper in American 
practice is from one-sixteenth to one-quarter inch to the foot on each 
side. One in thirty-six is the English standard. 

The upper 25 feet is one brick thick (8" or 9"); thickness increases 
by one half brick per 25 feet. If the diameter exceeds 60 inches, begin 
at top with one and a half bricks. 

An inner lining or core, detached from the wall proper and runnirfg 
either nearly to top or over 50 or 60 feet up, prevents expansion from 
cracking the walls. It need not be fire-brick all the way up, or even 
further than one-half. The core is made of tangent-laid brick, with an 
occasional header to guide the core by the wall. 

Another practice is to make a 100-foot chimney in three sections: 
first, 20 feet high, 16 inches thick; second, 30 feet high, 12 inches thick; 
third, 50 feet high, 8 inches thick. Core in three sections of 12, 8, and 4 
inches thick, respectively. 

The top of a chimney is exposed to weather and frost and snow, 
melting and freezing. There should be a cast-iron cap, or a stone, to 
protect the top edge of the brick. Large molded terra-cotta or fire- 
clay blocks are also used, clamped and doweled together. 

Cylindrical steel chimneys of riveted plate steel, secured by a flare 
in the lower 10 to 25 feet to a cast-iron base-plate, which again is 
anchored by heavy foundation-bolts to a masonry foundation, require 
no guy or stay ropes and are 35 to 50 per cent cheaper than a brick stack. 
They take less room, are strong and safe, and no air leaks in to cool the 
gas. They are brick-lined part way or all the way up. They must be 
kept painted. 

Stacks when not anchored to foundations by bolts, and all light and 
unlined stacks, require to be stayed by guys of wire rope. They are 
attached opposite the center of effort of the winds, at two-thirds of the 
height; are usually four in number, the first being led in the direction 



202 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

of the most violent wind, and each guy of a cross-section in square inches 
one-thousandth of the exposed area in feet. 

Skeleton chimneys have been put up by iron-works, but have no 
advantage over steel cylinders, and for many reasons are not as good. 
Brick is built in between uprights of rolled iron, which are banded by 
flat rings on the outside. 

Access should be permitted to the chimney at its base through a 
proper door either in the flue or in the foundation of the chimney, 
and it is best that a ladder on the outside of the chimney should give 
access to its top. In a square chimney this ladder can be made by bars 
let into two walls at a corner. Figs, 196 a-c show chimney construc- 
tions and the proportions which have been found satisfactory, accord- 
ing to which the thickness may be reduced as the chimney attains height. 

137. Artificial or Mechanical or Forced Draft. It has been already 
pointed out (paragraf 107) that a movement of the air for combustion 
might be mechanically produced by a proper appliance for this pur- 
ppse (Fig. 2, Nos. 5, 9, and 49). 

A calculation of efficiencies shows that for heights of chimneys such 

are ordinarily used the mechanical methods of securing draft are the 
more efficient, so that it becomes a question of consideration whether 
the necessary air for combustion shall be furnished by a costly .chimney 
or group of them, or by a continuously running machine of some different 
type. Artificial draft can be secured by two general methods. The 
first type is that made familiar in locomotive practice, in which a rapid 
motion is given to the air to draw it out of the smoke-box so that the 
reduction of pressure within the latter shall cause a flow through the 
grates, fire, and tubes to equalize this rarefaction. This is called 
the induced-draft system, and as applied when fans are used, as in 
steamship practice, is illustrated in Fig. 197. 

The other plan is to cause a pressure of air in the ash-pit below the 
grate-bars so that the air will flow up through the fire, the setting, and 
flues by the excess of pressure which prevails in the ash-pit. This is 
called the forced-draft system, and is becoming more usual in high-speed 
marine practice. The movement of the air can be produced either by 
means of a steam-jet inducing a current of air to flow, or fans or blowers, 
either of the centrifugal or positive type, may be used. If the first or 
aspirating principle is used, the products of combustion must pass over 
the aspirating appliance. These gases are hot and possibly corrosive. 
The heat makes lubrication difficult, and almost excludes the use of 
apparatus where lubrication must be provided unless all bearing- 
surfaces can be without the flues which carry the gas. Protection 
against corrosion can be secured if proper trouble is taken, but where 






I S 



I I 



\% 



\ i 



? I 



4r+-a- 



i 




vMHl 



H^i"*^ 




55^ CITJ Z I V 



Fig. 196c. 



Fig. 196d. 




Fig. 196b 




I h 




20.3 



Fig. 196a. 



204 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

this is not guarded against the apparatus deteriorates rapidly. The 
forcing system has the fresh cool air pass through the forcing apphance, 
and has furthermore the advantage of maintaining a higher tension 
within the setting than prevails outside of it, so that there is little or no 
tendency for cool air to leak through cracks or porous brick work into 
the gas-currents. This is a difficulty present where the draft is done by 
aspiration. On the other hand, the pressure system makes a hot and 



ppinaR DECK 



R DECK 




Fig. 19/ 



gassy fire-room if there are places where gas can escape through cracks, 
doors, or elsewhere from within the setting into the room. Fig. 198 
shows Mr. John C. Kafer's closed ash-pit system, similar to that on the 
U. S. S. Swatara and Kearsarge. Since combustion is more efficient the 
denser the air used to effect it, the pressure system offers an advantage 
from this point of view, as compared with natural draft or the aspiration 
system. 



BOILER FURNACES, CHIMNEYS, AND SETTING 



205 



128. Advantages of Artificial Draft. It is to be said in favor of natural 
or chimney draft, that when the chimney is once built and paid for, the 
draft-machine costs nothing to run except the heat which is used for 
this purpose, and it undergoes little or no deterioration with use. 
Furthermore, in cities the necessities imposed upon the power plant to 
carry the products of combustion high enough up to create no nuisance 




Fig. 198. 

in its neighborhood compel a height and cost of chimney which make the 
consideration of artificial draft unnecessary, since the high chimney 
must be there in any case. Again, where the plant is so large that the 
cost of the draft-machine becomes considerable, or, what is the same 
thing, the cost of the expensive chimney becomes distributed over a 
large number of horse-power units, the advantages of artificial draft are 
not so apparent. 

Artificial draft, on the other hand, offers the following advantages: 

(1) The rapidity of combustion in the fire-box is not Umited by 
atmospheric conditions. With a demand for high steam-pressure and 
great capacity in a limited space the forced draft is a necessity, as in 
war-ship practice. 

(2) It is possible to increase the evaporative capacity of a given plant 



206 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

without other change than the velocity of the draft-machine. This 
increase may be either permanent or to meet sudden demands for steam, 
such as occur in street-railway practice at busy hours. With natural 
draft the chimney must be designed to meet the maximum requirement, 
and will be partly shut off at other times. 

(3) It is possible to burn inferior, cheaper, and smaller sizes of fuel 
with artificial draft, because a high pressure can be maintained which 
will force the necessary air through a compact body of fuel. 

(4) The draft arrangements are more portable than chimneys can be. 

(5) The plant is more flexible for changes in quality or size of fuel, 
and the desirable thickness of fuel-bed on the grates. Grate-bars can 
be altered more easily if this should be desirable. 

(6) Where high stacks are not made necessary the cost which they 
entail is avoided, or is obviated by a less cost of the draft-machine. 
The troublesome settling of massive stacks is avoided when foundations 
are difficult or defective. 

(7) Leakage of air into the setting does not occur with forced draft 
on the pressure system. 

139. Disadvantages of Artificial Draft. The objections to be raised 
against the artificial draft are: 

(1 ) The running cost of the machine. While it takes less coal than the 
chimney to do a given work, the fuel is not the only expense where an 
engine must be run, consuming oil and other supplies, calling for repairs 
and supervision, and the expense of the latter may be considerable. 

(2) The artificial-draft machine occupies space which can often be ill 
spared. 

(3) Running machinery, and particularly that at high speed such 
as most draft appliances demand, is rarely silent, is often noisy, and is 
liable to breakdowns which compel it to stop. 

It will be seen that chimney-draft is not liable to these disadvantages. 

The machine for causing the draft may be a centrifugal fan driven 
either by its own directly coupled engine or by a detached engine, or a 
revolving shaft, or by means of an electrical motor. The positive 
blowers will be driven by belts, or their own direct-coupled engine or 
motor, whether used for pressure or suction methods, and the steam-jet, 
which is the third appliance, requires no moving machinery when used in 
either system. It will be seen that each of these offers some advantages 
and disadvantages of its own. The fan method, if driven by belting, 
increases the running cost; and if electric current must be generated, the 
cost of its transformation must be considered. The steam-jet plan 
occupies very little space and is cheap to buy in the first instance. It is 
in most cases too noisy. If used as a forcing system, the steam passes 



BOILER FURNACES, CHIMNEYS, AND SETTING 



207 



through the fire and is objectionable. If used as a suction system, the 
steam goes out with the products of combustion and does no harm. 

The methods which have been used in marine practice to secure the 
necessary forced draft are either the closed ash-pit system, the closed 



Zcj- n "°^ Tjir ( ) 




Fig. 199. 




Fig. 200. 



fire-room system, or the induced-draft system. The combination of 
closed ash-pit system with the induced-draft system enables preheating 
of the air to be easily done before it enters the ash-pit. Figs. 199, 200 
and 201 show typical stationary arrangements. 



208 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

The artificial-draft system is a feature of the automatic stoker shown 
in Fig. 175 and in some others, and it offers the advantage that the 
steam-pressure can be made to act upon the draft machinery directly 
and produce a more prompt and efficient effect upon it than when that 
pressure acts upon the chimney only and through a damper-regulator 
(paragraf 125). The fall of pressure in natural draft can only open 
the chimney wide and attain at best the full effect of the entire chimney. 




Fig. 201. 

By acting on the machinery of artificial draft the fall of pressure can be 
made to stimulate combustion above the normal rate, and with great 
promptness. 

130. Smoke-prevention. The preceding discussion on the hberation 
of heat from a fuel for motive-power purposes would not be complete 
without a reference to the loss of energy which occurs when combustible 
carbon passes out with the products of combustion, and without having 
undergone complete oxidation at the desired point. When this carbon 
goes off as carbon monoxide there is avoidable loss. When incandescent 
solid carbon fails to meet oxygen under favorable conditions for its union 
with it, the extinction of the glowing particles forms them into lamp- 
black or soot, which particles color the products of combustion, and cause 
them to darken the air and to defile the surfaces which they touch. A 
smoke, in its exact sense, is a current of products of combustion fro«i a 
fire, in which the otherwise colorless gases carry finely divided particles 
of black carbon. This carbon, resulting from incandescence which has 
ceased, is practically incombustible at ordinary heats. It could have 
been burned, however, if the union with oxygen had taken place while 



BOILER FURNACES, CHIMNEYS, AND SETTING 209 

the carbon was in the nascent or favorable state of its first incandescence, 
and the effort of the designer and manager of the combustion must be 
directed to keep up the gases to the temperature of the ignition of the 
carbon, and with a full supply of oxygen at sufficient temperature 
to satisfy the carbon. Pure hydrogen combustions are normally smoke- 
less, because of the absence of solid matter in the flame. Such flames 
are usually non-luminous for the same reason. 

The various methods for smoke-prevention have been grouped under 
the following heads: 

(1) The supply of excess of air by steam-jets, inducing current which 
they warm, and supplying excess of warm air above the fire and behind 
the bridge-wall. The difficulty with these has been that, after distilla- 
tion of the gas is completed, after a charge of fresh fuel is thrown on the 
fire, this excess of air is not needed, and the products of combustion are 
cooled by the diluting oxygen. Attempts have been made to correct 
this by graduating the supply of fresh air by chronometric or other 
appliances, so that the excess should be cut off after such an interval as is 
usually needed for the first distillation of gas. 

(2) By the coking methods of firing. By these plans a large dead- 
plate was used, so that the gases should be distilled off from the fresh 
fuel before its combustion was really begun on the grate-surface proper, 
and when the coking was complete only fixed carbon remained to burn 
on the grate-surface proper when pushed back. The gas distilled from 
the fuel on the dead-plate passed over the hot fire, and was so warmed 
that it was ready to combine and burn. Alternate firing of the two sides 
of the furnace, or the use of two furnaces delivering into a common 
combustion-chamber which were fired alternately, belong to this same 
class (paragraf 117). 

(3) The methods belonging to the principles of mechanical stoking 
are smoke-preventing methods in that each part of the fire always 
remains in the same condition, and the fresh coal which distils off gas is 
received in the coolest part of the grate, and passes to the hotter sections 
only after the volatile matter has been distilled off and burned in passing 
over those hottest portions. 

(4) Gas and oil-firing are smoke-preventing methods, since when 
properly done the combustion ought to be complete, and no carbon 
should pass out of the setting except in the form of carbonic acid. It is 
to this group that those settings belong in which the actual combustion 
of the fuel containing volatile matter is done in a separate furnace and 
away from contact with the boiler. This makes a relatively smokeless 
and efficient apparatus, and will answer with coals which cannot be 
economically burned in any other way. 



210 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

(5) The down-draft furnace appears to be one of the most successful 
appliances for smoke-prevention with smoky coals. As satisfactorily 
applied it involves the use of two sets of grate-bars, one over the other, 




so arranged that the draft passes downwards through the upper and 
lower sets of bars, or else passes downwards through the upper and 



BOILER FURNACES, CHIMNEYS, AND SETTING 



211 



upwards through the lower. Each set has its own fuel, but the intention 
is that the gases shall be distilled off from the fresh fuel on the upper 




grate, and shall be drawn downwards to mix with the hot products 
escaping from the lower where the solid carbon is burning. B}^ this 
the temperature of ignition is maintained for the distilled gas, so that it 



212 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



shall burn with the abundant supply of warm air admitted for this 
purpose. Figs. 202 and 203 show boiler-settings of this type. 




(6) The use of fire-brick or similar refractory material for the furnace 
or in the combustion-chamber (Fig. 204). This becomes hot by the 
impact of flame and gas, and keeps the temperature of the gas up to 



BOILER FURNACES, CHIMNEYS, AND SETTING 213 

ignition. It imparts some of its heat to the boiler by radiation after it 
is once brought up to full heat. 

(7) Preheating of the air-supply by hollow walls or flue-boxes which 
the hot gases surround while the fresh air flows within them. 

The objections to most of the smoke-prevention devices have been 
that the introduction of such appliances diminishes either the economy 
or the capacity of the plant as compared with what it was when the 
chimneys were allowed to smoke. The excess of air, diluting products 
of combustion, explains a loss of economy and capacity, and the superior 
efficiency of the yellow flame heating by radiation, as compared with 
the colorless flame of perfect combustion, is also responsible in part 
for this result. The losses seem to be about 12 per cent of power or 
from 7 to 13 per cent of economy. 

The term smoke-consumption or smoke-burning is an improper one. 
Lamp-black once made is incombustible and cannot be burned. The 
products of combustion are often colored brown by the presence of 
tarry or similar combustible matters, and these will ignite if the tem- 
perature be made hot enough. It is possible to prevent appearance of 
smoke by catching it in water through which the products of com- 
bustion pass, and in which the carbon is thrown down. 

A standard of the degree to which a chimney offends in the matter of 
smoke has been proposed by Professor Ringelmann of Paris, and has 
met with general acceptance.* He proposed six grades, of which the 
zero was a white surface and No. 6 was a dead black one. The inter- 
mediate degrees were to be marked by a combination of black lines on a 
white background such that if held 50 feet distant from the eye the 
network would become a tone ranging from gray to black in definite 
stages. The network was on the following scale: 

Card 0. All white. 

Card 1. Black lines 1 mm. thick, 10 mm. apart, leaving spaces 9 mm. 
square. 

Card 2. Lines 2.3 mm. thick, spaces 7.7 mm. square. 

Card 3. Lines 3.7 mm. thick, spaces 6.3 mm. square. 

Card 4. Lines 5.5 mm. thick, spaces 4.5 mm, square. 

Cards. All black. 

Fig. 205 shows a small area of the four intermediate grades, and in 
Fig. 206 is a reproduction originated by Professor Breckinridge of what 
these colors mean when compared to a smoke-plume. f 

* Transactions A. S. M. E. 1899, Vol. 21. 

t How to burn Illinois Coal without Smoke, L. P. Breckinridge, Univ. of 111. 
Bulletin, 1907. 



214 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 















































































































































No. 1 


T 


T 
















■ ■ ■ 




■ ■ I 




■ ■ I 




■ ■ I 




I ■ I 




■ ■ 1 




■ ■ 







^ 








" 


" 


" 


™ 








































































































































































































































































No. 2 




No. 3 N0v4 

Fig. 205. 



BOILER FURNACES, CHIMNEYS, AND SETTING 



215 



131. Boiler Setting. Side Walls. The internally-fired boilers are 
ready to use as soon as they are located and properly supported (the 
Cornish and Lancashire excepted). The externally-fired boilers and 
these two examples of the former class require a structure to be erected 
which shall support them and shall provide a proper place for the fire 
and some of the flues or spaces for combustion. This structure is called 
the boiler-setting. It must be of a refractory material to withstand 
heat, and of a non-conductor for heat so as to cause least losses by radia- 
tion. Its material must be easily manipulated to form flues of proper 
shape and character, and must be one with which it is cheap to build. 




Fig. 206. 



These conditions are best met by the use of brick. Those parts 
exposed to fierce action of heat will be of fire-brick, and the rest of the 
cheaper common red brick. The fire-brick may be used as an inner 
lining on the fire-surfaces for the more massive walls, provided proper 
care be taken in bonding the two grades together. The fire-brick is a 
little larger than the common brick, which may cause trouble in uniting 
them. Bridge- walls and the thin parts at the front of fire-boxes will be 
of fire-brick altogether. Cheapness can be secured by using fire-brick 
only above the fine of grate-bars both in the fire-box and behind it, 
but it is a question whether this is worth while. The fire-brick lining 
need not be carried very far into the chimney with anthracite fuels, 
since the gases should never be above 600° F. after they leave a properly 



216 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

set tubular boiler. With some sectional boilers the gases may be hotter, 
and with bituminous or long-flame fuels flaming may occur within the 
chimney, making a fire-brick Hning desirable all the way to the top. 




The thickness of the walls will depend in part on the methods used to 
support the boiler. If the setting of brick is to support the boiler and 
its contents, it must be at least a brick and one-half thick (12 inches), 
and will be more, usually 17 or 21 inches for outside walls. The twenty- 



BOILER FURNACES, CHIMNEYS, AND SETTING 217 

one-inch wall is usually made with a two or a four-inch air-space between 
two eight-inch walls. This makes a non-conducting wall for the sides^ 
and with considerable stability, because at intervals a brick is laid 
stretcherwise to act as a buttress in the air-space, and at other intervals 
a header-brick in each wall is laid to project across and touch the other 
wall without entering it (Fig. 208). The hollow wall has less meaning 
in walls between the boilers in a battery. Such walls will more usually 
be solid, and probably twelve inches thick. 

If the boiler is supported upon an iron framework independent of 
the brickwork as in the case of sectional boilers in the main (Figs. 134 
and 216), the brickwork of the setting becomes a mere shell to retain 
the heat and gases, and may become an eight-inch solid wall or a 
twelve-inch wall with air-space. 

Rear walls which form a sort of reverberating surface require to be: 
thick and well laid, because exposed to the deteriorating effect of heat 
in a marked degree. It is more usual to make these soHd or without 
air-space, and depend for coolness upon the non-conducting quality 
of brick. 

The use of lime-mortar in boiler-settings is not to be commended. 
The heat tends to calcine the lime, or continually to unset or loosen the 
mortar bond, and the effect of hydrating the .calcined lime is to injure 
the iron which it may touch. Fire-clay mortar is refractory and harm- 
less, and will be used in any case with the fire-brick work. 

133. Buck-stays and Tie-rods. The heat of the fire and its gases 
causing expansion and deformation of the setting, to which the expan- 
sion of the boiler and its supports may add their influence, makes it 
necessary that the setting should be treated structurally like a heating- 
furnace, and tied together by means other than the bond of the brick- 
work. For this purpose tie-rods will be laid lengthwise (Fig. 215) 
in side walls, and will be used also crosswise between the side walls. 
The lengthwise tie-rods bear at the front on the outer side of the front 
castings, and at the rear either on buck-stays or large washers, against 
which they bear by means of a nut on the threaded ends of the rod. 
The side-wall ties bear on buck-stays (Fig. 208). 

The buck-stay is a vertical bar of cast or wrought iron, of a section 
adapted to resist transverse bending. They are used in pairs on oppo- 
site sides of the setting, drawn together by the tie-rods and binding 
together the section of the wall against which they bear. Usually 
there are three pairs in the ordinary length of a boiler-setting. Their 
section may be a T iron, with the flat of the head against the wall 
(Fig. 215), or any convenient structural section may be used. Old 
rails used in pairs will be met quite often. Tie-rods need not be used 



218 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

at the bottom of the setting, provided the feet of the buck-stays be 
let securely into the footings upon which the walls are built (Fig. 185). 
133. Hanging of Boilers. — The weight of a shell or sectional boiler 
is considerable, and when its contents of water are added, the method 
of carrying this weight requires to be carefully studied. 




Fig. 208. 



Two methods are usual. The boiler is supported at its sides at about 
the horizontal diameter, or it is hung from above by eyes and links 
attached to its upper part, and symmetrical to a vertical diameter. 

The first plan calls for projecting brackets or '' lugs " to be riveted 
to the shell along its sides, and giving strength sufficient to carry the 
weight. These lugs will be of cast iron or steel castings, either sohd 
or with the projecting part fitted to slide home in a socket made for it 
and fastened to the shell. The number of these lugs will be fixed by 
the length of the boiler. Two on a side is best if possible, since then 
every lug carries not far from one-fourth of the load, no matter how the 
boiler may be deformed by expansion. If there are three or more 
lugs on a side, then when the lower elements of the boiler lengthen, the 
end lugs Hft, and most of the weight is on the central pair; if the lower 



BOILER FURNACES, CHIMNEYS, AND SETTING 219 

elements shorten relatively, then the boiler lifts off the central pair and 
is carried at the ends. These changes in length come from impact of 
cold feed-water, or of cold air when the fire-doors are opened wide and 
suddenly. Figs. 207, 85, 215, and others show such lugs and their 
forms. , 

Recent practice has favored the use of steel plate forgings for the 
lugs. Fig. 209 shows the type designed to provide for the rollers, on 
which the bracket is to move in expanding. 

The other method of support calls for an eye on the top of the boiler 
(Fig. 134), or on the two sides (Figs. 70 and 212), into which a hooked 
link may be fitted, so as to hang the boiler to a pair of cross-beams 




Fig. 209. Fig. 210. • Fig. 211. 

of structural material, the latter carried either upon the side walls 
as abutments, or by metal columns independent of the side walls 
(Fig. 216). Sectional boilers may be hung from the top, from the 
sides, or from the bottom, as may be most convenient and preferred. 
Fig. 210 shows a bracket designed to take the rod and nut of the 
suspending link from the overhead frame or gallows, and Fig. 211 a 
suspension eye forged up from flat steel. 

The method of support by lugs usually depends upon the side walls 
to carry the weight. To prevent injury to the walls, the wall is fitted 
with plates under the lugs to distribute the load, and to furnish a sur- 
face for the motion of rollers of one-inch round iron inserted between 
the plate and the lug-surfaces at one end so as to allow a free end to 
move lengthwise in expanding and contracting without pushing the 
wall or deforming the shell (Fig. 179). The rollers may be omitted in 
Hght boilers, and the boiler allowed to sUde on the plate. This pushes 
the wall about, however. The end to be fixed is determined by the 
convenience of the attachments to the boiler. The locomotive boiler 
is fixed at the front to the cylinders and frames, and is free to move 
at the fire-box end; most stationary boilers are fixed at the furnace end 
and expand toward the rear. 

Expansion in suspended boilers is provided for by the suspending 
link, and by tins their expansion is independent of the brickwork. 



220 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

This is the great advantage of this method of hanging. The objection 
to it with large-diametef shell boilers is that the weight tends to make 
the flexible shell take an oval shape when pressure is low, while the 
internal pressure restores the cyUndrical shape when it rises again. 
The flexure of the longitudinal joints caused by these changes of shape 
causes grooving near the joints, to be discussed in a later paragraf 
(196). With shells of small diameter this trouble is scarcely felt. 




Fig. 212. 



With very long cyHndrical boilers the necessity for many points of 
support conflicts with the considerable changes of shape by heat in 
such long lengths. This has given rise to the methods of hanging by 
means of equahzing-levers over the transverse supporting beams 
(see Fig. 134), whereby each eye carries its proportion of load in every 
condition of shape; or the same result is approximated by using stiff 
spiral springs (like car-springs) under the nut on the suspending links 
which hook into the eyes. When the boiler curves itself lengthwise, 
the spring accommodates the excess of relief of load, without causing 
so much strain on the plates of the boiler itself. A skilful designer, 
•compelled to use long boilers, has cut them into lengths and Hnked 
them togther by flexible connections of copper tube (Fig. 16), in order 
to meet this serious trouble. 

134. Boiler-fronts. It would be possible to make the front part 
of a boiler-setting of brick, but it is not usual to do so, because the 
openings through it for access to the furnace and ash-pit, and to the 
boiler itself, would make troublesome and short-lived constructions in 
brick, and would make the door-fittings diflacult. Hence the use of 
cast-iron fronts for settings is universal, for their convenience and 
cheapness, for ease of fitting, and for the effect to the eye which as 



BOILER FURNACES, CHIMNEYS, AND SETTING 



221 



completed structures the boiler-settings can be made to produce. They 
will be made in one or two sections set up edgewise, and held in place 
by the nuts on the ends of the longitudinal tie-rods through the walls 
(Fig. 215). 

Boiler-fronts are either full fronts or half fronts. The full fronts are 
sometimes called flush fronts, and the half fronts are also called exten- 
sion or overhanging fronts. The full or flush front will be used always 




Fig. 213. 



with sectional boilers, usually with tubular boilers, in which the prod- 
ucts of combustion are to be carried backwards over the top of the 
shell to a chimney behind the boiler, and quite often where the gases 
are to be taken from the front end of the boiler to a chimney by 
means of a sheet-iron duct. When the full front is used the side walls 
will be carried up level with the top of the front (Fig. 207), and the 



222 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

joint between the side walls over the boiler will in this case be made 
either arching, or by means of filling in on top of the boiler with some 
non-conducting material. 

The half fronts will be used where the side walls are to be carried up 
to the height of the supporting lugs only, and the smoke-box is to be 
made an integral part of the boiler itself (Figs. 215 and 185). A cyhnder 




Fig. 214. 



of a relatively light boiler-plate is secured to the shell of the boiler 
itself and, projecting beyond the plane of the front, forms a smoke- 
box independently of it. This arrangement is shown in Fig. 215. It 
implies of necessity that the gases are to be taken off from the smoke- 
box either directly to a chimney-stack or by means of a sheet-metal 
flu'e or breeching. 

There will be three sets of openings to be made in the boiler-front, 
each of which must be closed by proper doors. In the full or flush 



BOILER FURNACES, CHIMNEYS, AND SETTING 



223 




224 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

front these three openings are all made in the front proper. In the 
half front the two lower ones will be formed in the front, and the upper 
will be a part of the structure of the extension smoke-box. The top 
of the front is then curved to match the curvature of the shell or smoke- 
box which protrudes beyond it (Fig. 182). The lowest opening gives 
access to the space below the grates, which is called the ash-pit. The 
doors which close it are called the ash-pit doors. These doors are a 
means of controlhng the draft of air which passes up through the 
fire, and will be closed when the fire is to be checked. From examina- 
tion of Figs. 208 to 215 it will appear that such doors may be either a 
single large door, two smaller doors closing a large opening, or two 
independent openings, each with its own door. The advantage of small 
doors is the diminished strain on the hinges when such doors are 
opened, and the fact that such short doors are less in the way than 
long ones. It is not unusual to make register-openings in these doors, 
but they have comparatively small significance, since it is much easier 
to leave the door slightly open if but a little air is desired. 

The second set of doors open into the furnace or fire-box on a level 
above the grates, and each will be called a fire-door. Its function is 
to give access to the fire for charging it with fuel and for cleaning, and 
it also has a use in the control of the fire, since by leaving it open cold 
air from the fire-room enters above the fire, lowering the temperature 
of the hot gases by dilution and actually serving to cool the boiler, 
while at the same time the easy passage of air over the fire checks the 
draft through it. The same considerations as to the use of one large 
or two smaller doors are to be noted with respect to the fire-door, but the 
latter requires that it should give access for coaling and cleaning to 
every part of the grates, and consequently with a wide furnace two 
doors become a necessity. They have the further advantage that in 
coaling and cleaning they need not both be open at once. The single 
door is better than two doors which overlap, when it is possible to use 
it, because it closes the fire-opening somewhat more tightly. The 
minimum width of a fire-door should permit the easy handling of an 
average coal-scoop, which measures for small coal 14 inches across. 

The fire-door furthermore requires a special construction to prevent 
its becoming unduly hot by radiating heat from the fire. This is done 
by forming an air-space between the outer surface, which is the door 
proper, and the inner plate of perforated iron which is fastened to the 
door with distance-pieces to keep them at a fixed distance apart 
(Figs. 213 and 214). The inner or baffle plate receives the heat of the 
fire, and the circulating air between the baffle plate and the door 
serves to carry off some of the heat. The fire-door is often also made 



BOILER FURNACES, CHIMNEYS, AND SETTING 



225 



with register-openings to permit a certain amount of air to enter this 
air-space and so reach the fire above the grates. It is difficult to 
provide sufficient area to make these openings serviceable to supply 
oxygen for combustion, but the old rule used to be that such openings 
should be 2 square inches for each square foot of grate-surface with 
short-flame fuels, and 5 square inches where the fuel contained much 
volatile matter. The real use of air above the fire can be best obtained 
by leaving the door slightly open when it is required. 

The third set of doors will be called in shell boilers the flue-doors, 
and are intended to give access to the front of the boiler for cleansing 
the flues or tubes and for inspection. In full fronts and with boilers 
of large width it is desirable to make these doors double in order to keep 
their weight down. They will then be arranged to open on vertical 
hinges, and will be held shut by a common latch. In extension fronts 
it becomes more convenient to make the opening to the smoke-box 
for inspection by a door turning upon a horizontal hinge at about the 
horizontal diameter. 

135. Concluding Comment. Gallows-frame Supports. The typical 
fire-tubular boiler burning solid fuel and with return of the hot-gases 
has been the form chosen in the foregoing 
paragraphs. The sectional type is always 
suspended from transverse girders by ten- 
sion rods, and with the increasing use of 
concrete foundations this so-called gallows- 
frame support is coming more to the front. 
With concrete footings going down some 
distance into the ground, the Francis rule 
for area of adequate support is: . 

With hardpan, allow load per sq. ft. of 8 tons; 
With gravel, allow load per sq. ft. of 5 tons; 
With clean sand, allow load per sq. ft. of 4 tons; 
With dry clay, allow load per sq. ft. of 3 tons; 
With wet clay, allow load per sq. ft. of 2 tons; 
With loam, allow load per sq. ft. of 1 ton; 

which are larger values than are permis- Fig. 216. 

sible for chimneys (paragraf 125). The 

deep foundation in concrete enables the columns for the supporting 

girders to be cheaply made of steel pipe flanged top and bottom 

(Fig. 216) and buck-stays can be eliminated since the boiler does not 

tend to throw down the brick walls. 

The costly character of the chimneys and boiler settings required for 
the external combustion system of utilizing fuel energy (paragraf 2) 




226 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

are among the arguments used in favor of the internal combustion 
system as apphed in the gas or oil engine which has no boiler nor furnace. 
For further amplification of this the student is referred to other 
treatises.* It must not be overlooked, however, that in plants of any 
size using gas in the engine-cylinder made from a solid fuel, the cost of 
such gas-generator or producer and its process is an offset to the boiler- 
setting and chimney of the steam plant. The advantage is the conven- 
ient transmission of energy in the form of gas through pipes to the 
point where power is to be developed. The use of liquid fuel or gas 
under a boiler in a setting as a means of getting fuel energy is of consider- 
able importance and will be treated in the next chapter. 

* The Gas Engine: — A Treatise on the Internal Combustion Engine using gas 
oil or other liquid hydro-carbon. By F. R. Hutton. John Wiley & Sons, New 
York, p. 163. Edition of 1908. 



CHAPTER IX. 

FIRING BOILERS WITH GAS OR LIQUID HYDRO-CARBON OR WITH 

PULVERIZED FUEL. 

136. Introductory. The introduction of gas or liquid fuel under the 
heating surface of a boiler by mechanical pressure does away with the 
hard labor of the fire-tender, and derives all the other advantages of 
mechanical stoking (paragrafs 114 and 223) and introduces some 
advantages of its own. In the cities where natural gas has been intro- 
duced through mains and pipes to industrial establishments, the gas 
does not have to be manufactured, but interest on the installation of the 
pipes and gas-compressing plant must be paid for. Illuminating gas 
is too costly to be economically used for firing: fuel gas with less lighting 
power is the only one to be considered. 

With gas under pressure its velocity of flow can be used to draw into 
the burners the air necessary for combustion. The argand principle of 
tubular or hollow cylinders of gas with air both outside the sheet of 
flame and within it will be the basis of such 
burner design (Fig. 217). For hquid fuel ^ *^^' 
installations the oil must be broken up by 
atomization into a spray or mist, so that 
air shall meet every particle of fuel for 
quick and complete combustion. Such 
atomization can be effected either by send- Fig. 217. 

ing a jet of air or of steam through a film or 

thread of the hquid, or by breaking up the hquid mechanically by 
pressure into smafl threads or films. In any case an auxiliary is 
required to produce the pressure on the jet or burner before it can be 
started under the main apparatus. The same sort of burner can be 
used for either gas or oil, and in the discussion of advantages and 
difficulties, what is true of oil is also true of gas. 

137. Gas-flring of Boilers. The ordinary process of combustion 
means a gas-making in the fire-box and a subsequent combustion of the 
gas. But if the gas is made outside and led to the furnace, it is cooled 
in that process, and the heat of distillation and warming up the gas is 
lost, so far as the boiler is concerned. The cost of such boiler firing is 

227 




228 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

therefore greater than the firing cost from sohd fuel. The advantages 
are those of convenience, which are listed in the next paragrafs, rather 
than of economy, except where the labor economy is great. There are 
some liquid systems where the oil is first made into a gas before reaching 
the burner, either by passage through a heated coil of pipe (Archer) or 
other similar method. What is known as the Dutch Oven furnace is 
again a gas-firing system (Figs. 139, 140 and 204) since the philosophy 
of this system is the making of gas in the exterior furnace or fire-chamber 
and having it at so high a temperature by reason of the fire-brick arch 
at white heat over the fire that it shall be sure to ignite if oxygen enough 
at temperature enough can get to it. What is here lost is again some- 
what of the radiant heat of the hot solid fuel upon the heating surfaces, 
but in gaseous or flaming fuels this may be less than the gain from 
better combustion of the flames and gases. It is better than the remote 
or producer manufacture of the gas, and its bringing to the boiler in a 
comparatively cool state, since here all the radiant heat of the fire is 
lost, and some of that of the gas. If the gas is to be made at a distance 
and piped to the boiler, it is probably more economical to utilize the gas 
in internal combustion engines (paragraf 2) and bring the power by 
electrical transmission to the working point rather than to use the gas 
for making steam. If the heat of the combustion is desired for, heating, 
then the gas can be led in pipes to stoves where needed, and burned in 
such heaters directly rather than to burn the gas to make steam and 
carry the steam with attendant losses in condensation to the place to be 
heated. 

138. Liquid Fuel Burners. There are two systems for the combustion 
of oil: the liquid systems or the atomized vapor systems. The former 
is of no importance by reason of the advantages which attach to the 
latter. Fig. 218 shows a type approved in the U. S. Navy experiments 
in which the oil current is induced by steam, and Fig. 219 a form in 
which air is used. In Fig. 220 the moving steam jet carrying the oil 
draws in the necessary air by aspiration in an annular film forming 
a combustible mixture before it leaves the nozzle. In Fig. 221 is a 
type of the mechanical atomizer where the oil under pressure is forced 
through the spiral channels and is thus finely subdivided when it leaves 
the jet. This depends on meeting its air within the furnace. Fig. 222 
illustrates an oil-injector burner for locomotive use. By retracting 
the adjusting hollow steam jet, the nozzle can be swept out clean by 
shutting off the oil and blowing it through. The thimble at the 
nozzle passes the jet through the rear water-leg of the boiler. 

With respect to the use of air or steam for the inducing means to 
draw up and atomize the oil, it may be said on behalf of steam that 



FIRING BOILERS 



229 



it requires no air-compressing plant to bring it up to pressure for use 
under boilers, and there is not introduced^ into the flame a mass of 




Fig. 218. 



Fig. 219. 



inert nitrogen which must be heated at the expense of the oil-fuel, 
and acts to cool it. Steam is hot, furthermore, when it enters the flame, 




Fig. 220. 




and may be superheated. On the other hand, air must be introduced 
for combustion, and it is best to introduce it as the spraying and 
subdividing medium; steam dilutes the burning gas if it is not dis- 



230 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

Bociated; and if it is, the heat of dissociation is lost unless the tempera- 
ture is high enough for recombination. 




Fig. 222. 



Uptake 



139. Liquid Fuel Furnaces. The jet of burning oil and steam or air 
must not be allowed to impinge directly upon a heating surface of 
metal. Fig. 223 shows the usual furnace arrangement where the 

impact and scattering of the flow is 
against fire-brick set on edge. The 
grate is covered with asbestos slabs 
luted with fire-clay except where 
the air comes in. The bricks be- 
come white hot and serve to light 
the spray if it should chance to 
blow out. Or the grates may be 
covered with broken fire-brick and 
asbestos, through which air can 
pass, but which become hot enough 
to secure ignition. Great danger of 
explosion and fire is present if any 
mass of liquid oil or its resultant 
gas can accumulate upon the grate 
or in the setting. It must be assuredly ignited as fast as it arrives. 
A fire of coke is often used upon the grate to start the first ignition 




Fig. 223. 



FIRING BOILERS 



231 



and to keep up any ignition required subsequently. Such coke fire 
will burn very slowly upon a closed grate. 

140. Precautions in Oil-firing. Besides the danger with liquid fuel 
in external combustion just referred to, there are also the objections 
urg'ed in many places against the storage of any large quantity of 
liquid hydrocarbon in one place. Some cities limit the quantity 
which is allowed: others compel its storage below ground: or if above 
ground, then with a well or depression below it sufficient to receive 
and confine all the contents of the tank above. Crude oil or some of 
the volatile hydrocarbons make a combustible mixture with the air 
which filters into or enters the storage tank, so that water or street 
gas makes a safer displacing agent than air. The supply of fuel by 
gravity from any overhead reservoir of large capacity is objected to 
because the force supplying the oil cannot be shut off in case of 
accident which puts the shut-off valve out of service: and yet if steam 
or air is used in atomizing, it must never fall so low in pressure as to 
fail to atomize and thus flood the fire-box with raw liquid. 




Fig. 224. 



The arrangement of Fig. 224 shows a plant with the underground 
tank for storage and an oil standpipe to secure a constant head even 
with variable pump-action. The pump is steam driven at a speed to 



232 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

supply a little more oil than the burners can use, so that the stand 
pipe is always full and overflowing with a gentle pressure on the oil 
to keep any air from getting in the circuit. The oil is kept fluid in the 
storage tank by carrying the hot exhaust pipe into and through it. 
An air vent carries all vapor from the tank to a safe point outdoors 
and prevents any pressure or vacuum from establishing itself in the 
tank. C is the filling nozzle. To empty the standpipe back to the 
tank when atomizing steam is shut off or the pressure of steam falls 
below the atomizing point a weighted lever on the bottom of the stand- 
pipe leg is held up by a piston on whose lower side is the steam pressure. 
If the pressure on the piston falls below the safe and determined point 
the weight falls, opening the valve into the overflow back to the tank 
and emptying the standpipe down to a level below the burners, so 
that the pump dehvers back into the suction tank instead of to the 
burners. 

141. Advantages of Oil Fuel. Oil or liquid fuel offers many attractive 
advantages over the solid fuels. Many of these are those incidental to 
mechanical firing, to which oil lends itself easily, but besides these there 
are many others of its own. 

Mechanical handling of oil by pumps or aspirating burners gives the 
foHowing advantages: 

1. Economy of labor. One fireman by handling the necessary 
valves can manage eight to ten or more boilers of 100 horse-power each. 
With hand-firing of coal, one man can never manage more than four 
such boilers. 

2. No ashes, and their attendant labor and possible cost. 
Economy and convenience in oil-firing result from: 

3. No waste of fuel in ashes and cleaning of fires. 

4. No waste of fuel in banking fires overnight. 

5. No opening of furnace-doors for firing or cleaning. This is easier 
upon the brick-work of the setting, and on the metal of the boiler, by 
diminishing strains of sudden contraction. 

6. No injury from firing-tools in fire-boxes. 

7. No sparks pass out from a chimney, to set fire to combustibles 
outside. 

8. Absence of dust and ashes in fire-room and adjoining engine-room. 

9. Wide range of controllability of fire, not only within the limits 
of ordinary consumption, but beyond these. The fire is put out when 
demand for heat stops; an excessive demand for heat can be met by 
unusually great supply of oil. With solid fuel, a charge once made must 
burn itself out. In boilers, safety-valve waste is diminished. 

10. The greater calorific power of oil, and its controlled combustion, 



FIRING BOILERS 233 

enable more energy to be gotten from a plant whose capacity has been 
calculated upon a solid fuel basis. 

11. Smokeless combustion is more easily secured, and there is dim- 
inished loss of unburned carbon. 

12. Lower temperatures of fire-rooms, and lessened physical strain 
upon firemen. 

13. Absence of sulphur to corrode metal. 

14. Fires easily started. 

15. Economy of stowage and carriage of oil as compared with solid 
fuel. 

16. Economy of fuel-stations for navy or locomotive practice. 

17. No grates are required. 

If the heating power of oil be placed at 21,000 B.T.U. and that of the 
coal used for comparison be called 13,000 B.T.U. , a rule of three pro- 
portion will give 1 pound of oil as equivalent to If pounds of coal; 
or 1 gallon of oil equals 6.5 to 6.7 pounds of oil and will compare to 
12 pounds of coal; or 190 gallons of oil will equal a long ton of coal of 
2240 pounds. 

143. Disadvantages of Oil FueL There are objections to oil as a 
dependence for a source of heat. 

1. The use of crude oil with the volatile constituents in it is opposed 
by the health ordinances of some cities. In others the fire or insurance 
ordinances permit the use of oil only if the oil-tank is below ground, or 
so placed that it cannot flow out of its reservoir and carry flame to other 
buildings in case of conflagration. 

2. The vapor from crude oil is ill-smelling and makes an explosive 
mixture with air. It vaporizes even at low temperatures. 

3. If fuel-oil must be used, it is usually more costly than coal in 
most places. The problem is really to get the most heat-units for a 
unit of value. If the quotient of the calorific power of oil per pound 
divided by its price per pound at any point is greater than the same 
quotient for solid fuel, the oil is the cheaper.* 

4. The total oil-production of the world would supply but a small 
portion of the demand for heat as a source of energy. This would 
immediately affect the price of oil, if any large number of consumers 
were to decide to use oil. 

* If the number of pounds of oil per barrel be called B and be computed by 

multiplying the weight of oil per gallon by the number of gallons in a barrel, and if 

B be multiplied by the calorific ratio of oil to coal as above, and the product be called 

, ^- 2000 or 2240 •..,,, . , . , , 

A, then -j X price of oil per barrel = equivalent price of coal per ton, and 

A 
2000 or 2240 ^ V^^^ ^^ <^o^l P^^ ^o^ = equivalent price of oil per barrel. 



234 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

5. Most of the spray burners make an objectionable roaring noise. 

6. The surfaces exposed to an oil-flame usually become coated with 
a deposit of residue from the burning oil. 

7. Oil creeps past valves and leaks in a way which is annoying and 
may be dangerous. 

8. Explosions occur from the flame blowing out and igniting again 
with dangerous combinations of oil-vapor and air. 

9. Auxiliary apparatus in the way of a source of steam or compressed 
air is required for the burners; in starting, there must be a supply 
available of air or steam from a boiler or reservoir. 

The discovery of extensive oil-fields in the southwestern part of the 
United States has given fresh impetus to the use of oil in locomotives, 
with the special advantages of easy mechanical firing and sparkless 
combustion. Fig. 119 is of a boiler for this service. 

Both liquid and gaseous fuels, when the mixture of fuel and air is 
intimate, require no excess of air to dilute the products of combustion, 
and hence to cool the fire temperature (paragraf 110). 

143. Pulverized Fuel Systems. Designers have sought to secure for 
solid fuel or where liquid hydrocarbon was not available, the same 
advantages of rapid combination with oxygen and smokeless combus- 
tion by finely dividing the solid fuel and feeding it to the air-jet instead 
of the atomized oil. These are called pulverized fuel systems. The 
coal is ground between rollers to a fine or almost impalpable dust, and 
is led from a hopper through a feeding tube and forced into the furnace 
by the air which opens out and separates the particles so that air sur- 
rounds every one. If the temperature is high enough the combustion 
will be complete, exactly as in the flame from a fuel-bed in which the 
solid carbon particles have been separated by heat from the mass upon 
the grate. The condition for success is that the fuel shall be so fine 
that each particle shall be kept afloat in the gas current, without risk of 
its settling to the bottom before it has been completely burned; or that 
the velocity of the current of flame and gas shall not be so high that a 
particle of that mass shall not be completely burned before combustion 
must cease in tubes or around them when the latter are cooled by 
water. It is not convenient to pulverize and distribute to several 
boilers, for the material clogs and jams: it is best to pulverize at each 
boiler separately. The plant and labor and operation cost are serious 
offsets to the advantages. 

144. Sundry Special Fuels. In a parallel group to the pulverised 
coal systems are those in which sawdust is to be used. This is in 
effect pulverized wood. HoUov/ grate bars (Fig. 173) are practically 
a necessity here and forced draft (Fig. 225), to keep the fire from clogging. 



FIRING BOILERS 



235 



When the fuel in addition is wet or is not easily ignited as in the case of 
spent tan-bark or the woody refuse from ground sugar-cane (bagasse), 




Fig. 225. 

the further demand is made that the fuel be completely surrounded by 
heated surfaces and that distillation may proceed before ignition occurs. 
Hopper-feeding is an advantage for such material, giving it a slow, 




Fig. 226. 

regular, gradual feeding to the furnace area. Fig. 226 may stand for a 
t3^pe of such furnace with a sectional boiler, and the Myers furnace 
has been very successful in economy where it has been convenient to use 
vertical boilers. The fuel is fed into annular combustion chambers 
surrounding the central boiler at its base; the distillation occurs sue- 



236 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

cessively in the various sectors or furnaces, and the fuel is always kept 
at a high temperature until completely consumed. 

145. Conclusion. Heat Balance. In concluding this final chapter 
of that section of this treatise which has to do with the liberation of heat 
energy from the fuel and its transfer to the water in the pressure genera- 
tor, it may be serviceable to call attention to a convenient form of 
presenting the facts of the upper lines of Fig. 2 of a power-plant analysis. 
It is to present the items Nos. 2, 3, 4, 5, 18 and 19 as charge items in an 
accounting with the boiler, and to credit the boiler with its output in 
heat units both productive and non-productive. Such a statement 
of account has been called a '' heat balarxce " and its general form 
would be: 



HEAT BALANCE, OR DISTRIBUTION OF THE HEATING VALUE OF THE COM- 
BUSTIBLE. 

Total heat value of 1 pound of combustible B.T.U. 



1. 



2. 



3. 



Heat absorbed by the boiler = evaporation from and at 212 

degrees per pound of combustible X 965.7. 
Loss due to moisture in coal = per cent of moisture referred 
to combustible ^ 100 X [(212 - t) + 966 + 0.48 (T - 212)] 
{t = temperature of air in the boiler-room, T = that of 
the flue gases). 
Loss due to moisture formed by the burning of hydrogen 
= per cent of hydrogen to combustible -^ 100 X 9 X 
[(212 - + 966 -f- 0.48 (T - 212)]. 
4.* Loss due to heat carried away in the dry chimney gases = 
weight of gas per pound of combustible X 0.24 X (T — t). 

CO 
5.t Loss due to incomplete combustion of carbon = -^^ p^ 

per cent C in combustible 
X :^ X 10,150. 

Loss due to unconsumed hydrogen and hydrocarbons, to 
heating the moisture in the air, to radiation, and unac- 
counted for. (Some of these losses may be separately 
itemized if data are obtained from which they may be 
calculated.) 

Totals 



6. 



B.T.U. 



Per Cent. 



100.00 



* The weight of gas per pound of carbon burned may be calculated from the gas analyses as 
follows: 



Dry gas per pound carbon = 



11 CO, 4- 8 O -F 7 (CO + N) 



in which CO,. CO, O, and N are 



3 (CO2 + CO) 

the percentages by volume of the several gases. As the sampling and analyses of the gases in the 
present state of the art are liable to considerable errors, the result of this calculation is usually 
only an approximate one. The heat balance itself is also only approximate for this reason, as 
well as for the fact that it is not possible to determine accurately the percentage of unburned 
hydrogen or hydrocarbons in the flue gases. 

The weight of dry gas per pound of combustible is found by multiplying the dry gas per 
pound of carbon by the percentage of carbon in the combustible, and dividing by 100. 

t CO2 and CO are respectively the percentage by volume of carbonic acid and carbonic oxide 
in the flue gases. The quantity 10,150 = number of heat units generated by burning to 
carbonic acid one pound of carbon contained in carbonic oxide. 



I 



FIRING BOILERS 



237 



Of two appliances for utilizing heat energy, that is the more effective 
which most completely renders the available heat into useful work or 
product. Examples of the distribution of the available heat as reported 
by various authorities are given in the following table : 



DISPOSITION OF HEAT IN STEAM-BOILERS. 



Disposition of Heat 



Waste in flue-gases, including 
evaporation of moisture in coal 
and heating vapor in air when 
these losses are not separately 
given 

Evaporating moisture in coal. . . 

Heating vapor in air 

Imperfect combustion 

Clinker and ash 

Radiation and heat not other- 
wise accounted for 

Heating and evaporation of water 



Authority. 



Bunte. 



18.6 
3.5 



8.0 
4.1 

7.6 

58.2 



Scheurer and 
Meunier. 



5.5 
2.5 



6.0 



23.5 
61.0 



14.8 
6.1 



13.4 
65.7 



Donkin and 
Kennedy. 



9.4 
0.1 



13.9 
63.8 



22.5 
0.1 



0.0 
0.2 

11.0 
66.2 



6.5 
0.0 



0.0 
0.0 

15.0 

78.5 



Head- 
lev. 



5.04 
1.55 
0.18 
1.44 



4.00 

87.79 



An interesting computation of the results and requirements with a 
combustion of 100 pounds of anthracite is given in the following table, 
where it is assumed that the coal and air have a temperature of 60° and 
that the chimney-gases are at 500°. Hot ashes are withdrawn at 450°, 
and 2 per cent of carbon goes out with them. Under the assumed 
conditions 21 per cent is lost, for which ash and moisture in coal and 
air are responsible for over 5 per cent. 



HEAT 



LOSSES INCIDENT TO THE COMBUSTION OF 100 POUNDS ANTHRACITE 

COAL. 



Heat-losses. 


Number 
of B.T.U. 


Per Cent 

of Total 

Heat of 

Fuel. 


By water = [ (212 — CO) X wt.] + 965.7 X wt. + [sp. heat 
"X (500 — 212) X wt] . 


37012.5 
27994.2 
158452.8 
21973.6 
1105.7 
29488.3 


2 83 


By carbonic acid= wt.X sp. heatX (500- 60) 

By nitrogen=wt Xsp heatX (500— 60) 


2.13 
12.07 


By free oxygen=wt.Xsp. heatX (500— 60) 


1.67 


By ash=wt.Xsp. heatX (450—60) 


0.08 


By carbon in ash=wt.Xsp. heatX (450-60) + wt.X 14650 

By carbonic oxide— wt Xsp heatX (500— 60) + wt X4400 


2.24 








Total heat lost exclusive of loss by radiation 


276027.1 
12 


21.02 


Theoretically possible evaporation in pounds of water from 
and at 212° per pound of combustible utilized 


.73 


Theoretically possible evaporation in pounds of water from 
and at 212° per pound of fuel utilized ... 


10.44 









238 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



Entering 
furnace. 



100 lbs. 
of coal. 



1929.83 lbs. 
of air. 



Pounds. 
Water 2.00 

Ash 11.50 — I 

Carbon 82.0o| ~ 

2.00 

1.60 

0.9a... 



Hydrogen 
Oxygen . . 
Nitrogen .- 



Oxygen for CO2 . . 
Oxygen for HgO. . 
Oxygen forCO. . . 



213.33- 



14.40— 
00.0 
Oxygen free ...... . 227.73= 



"!! 



I •: 



Waste Products in CHiMNEt. 



! li 



-:-Steam 



Pounds. 
29.50 



i-CO. 293.33 



Nitrogen 1474.37... 

Water 9.50 — 



— [ j..Nitrogen. . 1475.27 

' ■ '"^ 00.00 



Oxygen . . 227.73 



Per Cene 
by Wt 

1.46 
14.4S 

72.82 
00.00 
11.24 



Waste. Products in AsH-T i¥r 



Carbon 



11.50 
2.00 



85.18 
14.81 



' Total Heat of Fuel, 
Weight of C X 14,650 = 82 X 14,650 = 



1,201,300 

Weight of H - C^^'f ^ ] X 62,100 = 2 - 1^) X 62,100 = 111,780 

1,313,080 B.T.U 



B.T.U. 
B.T.U. 



Heat Generated. 



80 X 14,650 = . , . . . 
2 - (^] X 62,100 



m 



1,172,000 
111,780 



B.T.U. 
B.T.U. 



1,283,780 B.T.U. 
and 15 



It will be apparent that the losses are due to Nos. 7, 8, 9, 13, 14 
of the analysis in Fig. 2 and may be listed as 



1. Losses in heat of ashes 

2. Losses in heating fire-room 

3. Losses in excess chimney temperature . . . 

4. Losses in an incomplete combustion 13- 

5. Losses in evaporating fuel moisture 

6. Losses in heating inert matter 



Nos. 10 and 12 are returned to the steam: Nos. 18 and 19 are partly 
returned, and what is not returned is not lost. 

Heat energy is expended after the steam is made in running some of 



FIRING BOILERS 239 

the auxiliaries discussed in later chapters, but for the purpose in hand 
and with regard to the boiler only, the above is reasonably complete. It 
will be for the later treatments to bring up the economy from use of 
auxiliary or subsidiary devices in diminishing labor expenses or dim- 
inishing heat consumption. 

It is conceivable that the balance of heat should not be a credit 
balance, or that the losses overbalance the input. This is so rarely the 
case that the reverse is the general case. If the plant were called on to 
make a financial balance of input of capital and labor and material, 
the credit balance on the heat balance computation, multiplied by 778 
to reduce it to foot-pounds and by the factors to change it into horse 
power per year, and again multiplied by the price of a horse-power per 
year, makes a product which is the income per year. The expense per 
year on the debit side will be the interest on the plant, deterioration, 
repairs, labor, fuel, supplies, water, and general expense. This is for the 
steam furnished to the engine; and the significance of the heat-balance 
factor is at once apparent. 



CHAPTER X. 

BOILER ACCESSORY APPARATUS. 

146. Introductory. It will be apparent from Figs. 1 and 2 and the 
logic of the development in the preceding chapters that the steam 
boiler as a generator of pressure from heat and a storage reservoir 
for energy requires for its safe and economical handling as well as for 
convenience that certain accessory apparatus should be applied to it. 
The water has to be fed into the boiler against the working pressure, 
and a pump or its equivalent driven by power would seem essential: 
the water must not be pumped in excess, else the generator floods 
with water, nor in too small quantities, else the metal of the boiler 
overheats. The control of the fire, too, must be related to the consump- 
tion of energy and steam by the engine, and there must be a relief 
valve to prevent accumulation of excessive pressure, and provisions 
for draining mud and dirt from the boiler when the feed-water brings 
it in and leaves it behind when it goes off as steam gas. . All these 
belong in a class of accessories which are essential and will be therefore 
present in any plant whatever. 

In addition to these, and forming a separate group, are certain 
pieces of apparatus which may be called auxiliaries to distinguish them 
from the essentials. These are to secure economy of labor or economy 
of heat utilization, and are to be described as desirable but not indis- 
pensable. In this class are the coal-handling and ash-handling 
machinery, the low-water alarms, fusible plugs, feed-water heaters, and 
the like. The present chapter is to treat of the essential accessories, 
leaving the auxiliaries to a later chapter. 

It must not be inferred from the word " essential " that no plant can be 
run without these. Plants were so run before they were introduced, 
and can be still run when these are disabled. But it is so much better 
to have them that it is foolish and wrong to try to do without them. 

147. The Feed-Pump. It will have been obvious from Fig. 1 and 
from the requirements of the case that an apparatus to force water 
into the boiler or pressure generator in an essential. Nos. 18, 19, 20 
and 21 of Fig. 2 show the place and function of the water-supplying 
machinery. In the beginning, when pressures in the boilers were low, 
water could be gotten into the boiler by gravity from an elevated tank 

240 



BOILER ACCESSORY APPARATUS 241 

(Appendix, Fig. 697 A) : in a few cases where the city mains carry- 
water at high pressure no separate pump for the boiler may be required; 
but in this latter case the water- works pump is the boiler-feed pump. 
Such pump as the boiler requires is to feed to it the water which it 
evap'o rates, and is hence called the feed-pump, and all its accessories are 
designated by the same prefix. The suction of the feed-pump comes 
from a well or cistern or pond or water-course or from the municipal 
water supply. Its quality is the main element, and this will be taken 
up further in Chapter XII. If it is desired to doctor the feed-water or 
to physic the boiler by introducing reagents for a chemical reaction, 
they are introduced into the suction tank, or by a branch inlet into 
the suction pipe. The cross section of the pipe should be such that 
the water should not be compelled to flow in it at a lineal rate faster than 
200 feet per minute. The suction pipe rarely has valves in it, unless 
the supply comes under pressure or from several sources, so that at 
times an isolation of any source becomes necessary. The prime requisite 
of the feed-pump is that it shall supply the quantity of water needed, 
and deliver this quantity into the boiler against the pressure therein, 
and overcome all frictional resistances of valves and piping between 
the suction tank and the boiler. This quantity of water per hour is at 
least the maximum evaporative capacity of the boiler-heating surface, 
or the maximum water consumption per hour of the engine (paragrafs 
8, 9, 11, and 12). It is usual to make it 125 per cent of this maximum, 
to allow for losses of steam in leakage at the safety valve or whistle, 
and to enable a quantity of water and heat to be accumulated in the 
boiler while the continuous demand is being made, if this should be 
desirable. A strong feed of cool water is an effective way of lowering 
pressure or keeping it down. 

The feeding power may be given by a pump or by an injector. If 
a pump is preferred, it may be used in several ways. 

148. The Attached Pump or the Independent Feed-Pump. By the 
term " attached " pump is meant the type in which the power for 
the pump piston or plunger is derived from the main engine, or the 
pump is attached to its mechanism. It was first driven in early vertical 
beam engines from one of the rods actuated by the beam of the engine 
mechanism: it was later in horizontal engines driven from the cross- 
head or crank-shaft. It is often in factories driven by a belt from tbe 
shafting of the transmission machinery (Fig. 230). The advantages for 
the attached plan are: 

1. The feeding is constant in small quantities per unit of time. 

2. The feeding is persistent or without pauses, and needs only to 
have quantity controlled by an attendant. 



242 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



3. The feeding by such control can be kept proportional to consump- 
tion or the water level constant in the boiler. In theory, the pump 
should at each stroke send into the boiler the same weight of water 
as went out of it to the engine in the form of steam at the previous 
stroke. 

4. The big engine cylinder will use the little extra steam required 

to work its pump with more econ- 
omy than the Httle independent 
cylinder operating the same pump 
cylinder. 

The objections are: 

5. The system cannot be used 
in direct form on very high speed 
engines. 

6. The pump only works when 
the main engine is running: or the 
whole power plant, as in a loco- 
motive, must be run in order to 
work the pump. 

7. The control of the feed cannot 
be on the delivery or forcing side 
of the pump, but must be on the 
suction side. The power of the main 
engine could break the pump and 
fittings if the water could not get 

away from the pump-barrel. To control on the suction side means 
a partial filling of the barrel when the suction valve is not wide open, 
and hence a thump or pound when the piston or plunger fetches up 
against solid water just as the valves open from the pressure. 

When driven from the main engine mechanism directly these pumps 
are usually plunger pumps, giving their volume by a long stroke and 
relatively small diameter. 

A system of control much used with the attached system is to place 
a branch outlet on the delivery pipe from the pump, with a valve on 
it, controlling the discharge through that pipe which leads back to the 
suction-tank or to some outfall to waste or overboard. When the branch 
or by-pass valve is wide open, all the pump delivery will go that way 
against the less resistance and none will go to the boiler. When the 
branch valve is closed, all the feed will go to the boiler. At partial 
openings some goes to the boiler and some by-passes through the 
valve according to the relation of resistances in the two pipes, but at 
no time can the resistance or pressure in the pipe exceed that due 




Fig. 230. 



BOILER ACCESSORY APPARATUS 243 

to the pressure in the boiler. Fig. 230 shows an accepted form of shaft- 
driven pump, capable also of being attached to an electric motor in 
the next class. 

The Detached or Independent Feed-Pump is one driven by its own 
independent power, and not from the main engine directly or indirectly. 
This may be a steam pump or an electric pump or get its power from 
any source. Its advantages are: 

8. It can be run at any speed of its own, not limited by the high 
speed or the low speed of the main engine. 

9. It can be located anywhere. 

10. The main engine does not have to be run to pump water. The 
pump can be run by hand if desired. 

By running the pump at a slow speed and controlled by its power, 
the advantages 1, 2, 3, and 4 of the other system are secured. 

11. In large plants several feed-pumps in duplicate can be operated 
so as to lessen danger of a complete stoppage by a break down. 

If steam is used to drive the pump, the objections are: 

12. The uneconomical use of steam in small cylinders: 

13. The disposal of the exhaust from the steam-cyHnder, and the 
drips. 

14. The running expense of the pump in oil and supphes. 

The electric motor-driven pump secures the variable speed advantages 
of Nos. 8 to 11, and the four advantages of the attached system. Its 
current costs more than the steam of an economical engine, but less 
than that of a wasteful one. In very large plants the feed pump 
becomes large enough to secure some economy in steam consumption 
by compounding and expansive working (paragrafs 298, 317). The 
electric pump is easily governed so as to be partly or largely auto- 
matic in action: it will usually be multiple-barreled to secure constant 
flow and equable resistance to the motor. 

Independent pumps may be either plunger or piston pumps. The 
piston is lighter in weight and is supported through its entire traverse: 
it will be more usual with clean waters. The plunger is at its best 
with gritty waters since it does not touch the bore of its barrel on 
the bottom where the sand Hes. Massive plungers are best used in 
vertical engines since they then produce no tendency to flexure as 
they are moved in and out. When the plunger system is made 
double-acting, it may either pass through a partition in the pump 
chamber (Fig. 231); or the two plungers may enter opposite ends of 
the chamber with the partition between without an opening but the 
plungers connected outside by a pair of rods; or the plunger may slide 
in and out of a pair of separate chambers (Fig. 232). With these 



244 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



latter arrangements the plunger packing is external and accessible: 
with the piston or internal partition leakage may take place from end 
to end. It does no special harm except to increase the " slip " of the 
pump, or the difference between the water actually pumped and the 
computed volume of the plunger displacement per minute or per hour. 
The steam power may be applied to the pump in two differing 
systems. In the one a fly-wheel is used to control the speed and a 

crank and connecting rod or its 



/-\ 




equivalent to control the length of 
the stroke. The, fly-wheel carries 
the piston past the dead centers so 
as to operate the valves effectively 
and prevent a stalling of the pump 
with the valve covering the ports 
to both ends of the cylinder. The 
other is the non-fly-wheel non-crank 
pump or the direct-acting pump. 




Fig. 23L 



Fig. 232. 



Both are direct-acting, but this term is used to distinguish the types 
from each other in popular use. 

149. The Fly-wheel Pump. The fly-wheel feed-pump horizontal or 
vertical resembles a typical steam-engine mechanism, having the pump 
barrel on the prolongation of the steam-cylinder piston-rod (Fig. 233). 
Instead of the yoke scheme for eliminating the connecting rod and the 
room it occupies, a short rod is often used in fire-engine practice which 
turns the crank within a frame in the plane of the rods which gives the 
necessary swing for the short crank which is required (Fig. 234). The 
power does not go through the crank but only the forces of regulation 
by means of stored energy in the fly-wheel. The vertical fly-wheel 
pump used for feeding boilers on the Mississippi valley rivers has been 
called a " Doctor." The advantages of the fly-wheel principle are 

(1) It is simple and positive in its action. 

(2) This adapts it for use where only unskilled labor is to be had. 



BOILER ACCESSORY APPARATUS 



245 



(3) It secures economy of steam-consumption by its ability to work 
the steam expansively. 

(4) Its stroke is a positive length determined by the crank, and if 
necessary it can be worked as a hand-pump by turning the fly-wheel. 




Fig. 233. 



(5) Its valve gear is very simple and obvious, and its stoppage 
from any clogging of ports unlikely. If there is pressure in the steam 
pipe and valve chest, the pump must run. 

The objections to the fly-wheel pump are 

(6) It cannot be run slowly without danger of 
stopping on its dead centers, unless duplex and with 
cranks quartering. Then it can be kept down to 
20 turns a minute. 

(7) It cannot be conveniently controlled, there- 
fore, by valves upon the delivery-pipe from it. 

(8) The objection which has been urged against 
fly-wheel pumps that they accelerate the flow of 
the water through the pump-cylinder as the velocity 
of the piston is controlled by that of the crank, 
has no significance with the relatively small masses 
of water which these pumps are required to 
handle. Fig. 234. 

150. Direct-acting Pump. The direct-acting pump differs from 
the fly-wheel pump by having no crank, shaft, or revolving wheel, but 
simply the steam-piston on one end of a piston-rod, and the pump- 




246 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

piston or plunger at the other (Fig. 235). Since there is no stored 
energy or velocity in a revolving or moving mass to carry the motion 
past the end of the stroke and cause the engine to reverse, this result 
must be otherwise attained. The energy in the reciprocating masses 




Fig. 235. 



of pistons and rods is not enough, since the friction of the pump and the 
resistance of the water will leave the piston in such a position that the 
valve attached to it positively will have so reduced the steam pressure 
on the forward stroke that the energy remaining in it will not carry it 
far enough further to open the port for the return stroke. This result 
is best secured by having the steam valve not directly or positively 
attached to the piston-rod, but by having such valve thrown from the 
forward to the backward position by another engine piston driven by 
steam, the valves of the latter being operated by the main engine piston. 
In the design of Fig. 235 the piston which moves the main engine valve 
is that of a purely auxiliary engine in the little cylinder on top of the 
steam-cylinder. The valve-rod is that of the auxiliary and not of the 
main cylinder. As the piston of the pump moves to the left for example, 
the valve of this large cylinder is at the left and the right-hand port 



BOILER ACCESSORY APPARATUS 



247 



wide open. It stays so until the piston in its traverse by its connection 
to the valve-rod of the auxiUary moves this valve far enough to cause 
that auxiliary piston to move from left to right carrying the main 
engine valve from left to right and opening the main engine left-hand 
port wide. The main engine thereupon makes its stroke and the cycle 
is repeated. The main engine can never stall on its dead-centers, no 
matter how slow it moves, for its steam valve is either wide open at one 
end or at the other, and such motion occurs while the engine piston is 
at rest and independent of it. The mechanism of the auxiliary engine 



Air Chamber 




Fig. 286. 



takes many forms as to its valve and the motion of its stem : the valves 
may be concealed in the cylinder casting and be operated by spindles 
pushed internally by the main piston. Or, in the duplex type, the 
auxiliary engine may become a second pumping engine cylinder at the 
side of the other one, and the valves of No. 1 cylinder be operated by 
the piston motion of No. 2 (Fig. 236). 

In this the steam valve shown is operated by the dotted lever; and the 
lever in full lines is connected to the valve stem whose end is dotted. 
The duplex pump gives a momentary pause at the end of each piston 
traverse while the other piston is moving its valve for it ; and this pause 
permits the water valves to seat quietly and without thumping and 
lessens slip. 

The advantages of a direct-acting or non-fly-wheel pump are 
(1) The velocity of the delivery is proportional to the resistance 
offered by the water. Hence it is possible to control the feed-pump of 
the boiler when of this class by the opening and closing of valves upon 
the delivery. When the resistance to the delivery exceeds the forward 
effect of the steam-pressure the pump stops. The forward or feeding 



248 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

force is secured by making the area of the steam end of the pump three 
or four times the area of the water end. 

(2) The pump has no centers, but will start from rest as soon as 
steam is turned on to it. This property is the result of the steam- 
thrown valve, because the main valve is open at one end of the cylinder 
until reversed and opened wide at the other end. 

(3) The pump can be run as slowly as suits the convenience or the 
requirements of the feeding. 

(4) Water in the cylinder from condensation causes no danger to the 
mechanism. The pump will start with water as well as with steam if 
the pressure is there. 

(5) The velocity of flow is not accelerated by the connection of the 
piston to revolving mechanism. 

The objections to the non-fly-wheel pump are: 

(6) That the steam-thrown valve does not encourage expansive 
working, nor at ordinary speeds can it be secured when there is no fly- 
wheel to store up excess of work at one part of the stroke to give it out 
at the second part. In large water- working pumping-engines this has 
been secured by devices which are not considered worth while for feed- 
pumps. 

(7) The stroke is not positive in length, as there is nothing to compel 
it to be so. 

(8) This compels an excessive clearance- volume in the steam-cylinder 
in order to guard against the piston fetching up against the head when 
running at high speed. 

(9) The ports or passages of the auxiliary engine in the single-cylinder 
type are small, sometimes tortuous, and are liable to clog or be made 
impassable. This comes from the lubricating oil, or from oxide of iron; 
or in making gasket joints between parts the port opening has been 
overlooked, and remains closed when the joint is made up. The pumps 
stop for no apparent or obvious reason, and this lends an appearance of 
complexity and mystery to their operation. 

The advantages where intelligent labor is to be had which belong to 
the slow running and easy control of the direct-acting pump have made 
it a very popular form for boiler-feeding. The fly-wheel type remains 
in general preference in Western river-boat practice and for fire- 
engines. 

It is not desirable to control a direct-acting pump by a valve on the 
suction, since the barrel of the pump should be perfectly filled at each 
stroke. Otherwise, when the pump reverses, part of the stroke will be 
made against little or no resistance, and as there is no controlling 
mechanism of crank and revolving shaft, a serious jar will occur when 



BOILER ACCESSORY APPARATUS 249 

the pump-piston encounters solid water after part of the stroke is com- 
pleted. 

For similar reasons when a pump is to handle hot water it should 
receive the water from a height caused by gravity, and not be compelled 
to lift it. The vaporization of the hot water under the reduced pressure 
caused by the sucking action of the pump will prevent the barrel from 
fining, entailing the same difficulty from jar. When pumping hot 
water, furthermore, the pump will require to be fitted either with 
metallic valves or hard rubber resistant to the action of heat. With 
cold water the ordinary soft-rubber valves closed by springs are cheap, 
convenient, and tight (Figs. 231, 232). 

These figures and Fig. 236 show also the usual arrangement of such 
valves, the suction entering by atmospheric pressure or gravity into the 
chamber under the lower set of valves at each end alternately and being 
forced out by the displacement of the piston or plunger through the 
upper valves at the other end. These illustrate also the two practices 
of a small number of larger valves, or a large number of smaller valves. 
Inertia effect is less as the masses of the valves are less. The use of a 
feed-water heater to save the waste-heat in the exhaust of the feed- 
pump will be discussed under Boiler-room Auxiliaries. 

151. The Feed-pipe and its Valves. From the pump to the boiler, 
the water must be carried in a pipe. This pipe must be strong enough 
to resist pressure and must not be easily corroded. It is often made of 
copper by reason of its flexibility and ductility under the changes of 
temperature to which it is exposed, and because bends are easily made 
in it, and because the solid matter precipitated from the water does not 
adhere to it. Iron pipe, which is often used in stationary practice, has 
the advantage of being cheap and that the fittings which are required 
are easily made and attached to it, which is 

not the case with the copper feed-pipes. The ^^^ Ms ^. ^^^ ^^^ 

diameter of the pipe should be chosen first /^^^^^^^^^^^^\ 

water through it not exceed 200 to 400 ^^^^^ C ?*rJ H BP j 

desirable also that the feed-pipe should be ^^^mBp^^^^^^^F 

large enough so that even if it should ^^^^^^^^^^^^ 

become somewhat stopped up with scale, as Fig. 237. 

has occurred in the example shown in 

Fig. 237, it may be possible to get the scale out, or to leave still space 

enough through which the water can be forced. 

Upon the feed-pipe will be the necessary valves. The first of these 
is one for controlhng the flow of feed-water into the boiler in question 



250 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

if a number of boilers are supplied through a common pipe. This will 
be through a cock-valve, which is preferred in English practice, or a 
globe valve, which is more usual in American practice. The cock- valve 
is not liable to clogging from precipitated scale, which is a difficulty 
connected with the globe valve, but with modern forms of globe valves 
they are easier to keep tight than a taper plug. The latter also gives 
trouble sometimes by expansion, although the packed-stem plug-valves 
are not open to this difficulty. Close to the boiler where the feed-pipe 
enters it will be a check-valve. This is imperatively necessary where 
several boilers are connected to a common feed-pipe, but is desirable 
in every case. The check-valve lifts by excess of pressure on its lower 
side, as compared with the pressure in the boiler, which bears upon its 
upper side.* Its object is to prevent water which has once gotten into 
the boiler from getting out again back into the feed-pipe. This serves 
to keep the scale out of the feed-pipe, to prevent siphoning of water 
from one boiler into another, and to prevent hot water from working 
back to the pump where it would be troublesome. These check-valves 
are made to work in horizontal or vertical pipes. The difficulty to which 
they are liable is a tendency to leak through abrasion of their seats, or 
by being held off the seat wholly or in part by some solid matter in the 
feed-water which gets caught in the valve. All such check-valves 
have an opening to permit access to the valve for inspection and for 
repairs (regrinding of the seat, or renewal of the valve-face) (Figs. 238 
and 239), and in order to permit this repair or inspection without 
emptying the boiler of pressure and of water it is desirable to interpose 
a gate or stop valve between the check-valve and the boiler, so that 
the latter can be cut off from the check-valve when it is to be inspected. 
152. Introduction of the Feed-water. The water to be evaporated 
by the boiler is fed to it as a rule cooler than the water within the boiler. 
It should therefore be introduced at such a point as to favor and not 
to impede the currents of circulation and convection within the boiler; 
and furthermore, if it can be persuaded to deposit the solid matter 
which is contained in the feed-water immediately on entering the 
boiler, it is desirable to have regard to this in selecting the place at 
which the water shall enter. In sectional and most of the shell boilers 
this indicates that the water should commence to flow within the boiler 
at or near the surface, and at the back of the boiler or where the heaviest 
water is descending. By having the feed-water enter at the surface 
there is also met less danger from the siphoning of the water in a boiler 
out through the feed-pipe either to another boiler or to waste, if any- 
thing is wrong with the check-valve which should prevent this action. 
Boilers may empty themselves through a feed-pipe which enters at the 



BOILER ACCESSORY APPARATUS 



251 




Fig. 238. 





Fig. 239. 



252 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

bottom; but where the feed-pipe is near the surface of the water, the 
water below its level can only get out by evaporation. This further 
produces less injury to the metal of the boiler near the feed-inlet from 
sudden change of temperature. 

It is more convenient, however, to have the valves control the flow 
of feed-water into the boiler at the front rather than at the back. This 
has given rise to a very prevalent practice of carrying the feed-pipe 
through the front head, and along the length of the boiler to that point 
farthest from the fire at which the water shall actually mix with the 
water in the boiler. This serves to bring this entering water up some- 
what nearer the temperature of the boiler-water before it strikes the 
shell-plates. This, inner feed-pipe is sometimes perforated along its 
length with the idea of causing the cold water to enter in fine streams 
rather than all at one place. The objection to the interior pipe, and 
particularly to a perforated one, is its liability to become stopped up by 
matter precipitated from the water by heat. 

The introduction of the feed-pipe and its details may be studied with 
advantage from Figs. 73, 74, 96, 126, 131, 148, 153, 178, 183, 185. 
Figs. 178 and 183 show the internal distribution arrangement. In the 
coil boilers the feed will be universally at the bottom end of the coil so 
as to make the current of circulation an unbroken one, and to permit 
the feed-pump to effect in part a mechanical circulation (Fig. 161). 
The exception is the White semi-flash coil, where the cooler water is at 
the top and the circulation from above downward (Fig. 165). 

153. Blow-off Pipe. The boiler requires to have a pipe connected 
to its lowest and coolest point to allow the boiler to be emptied for 
inspection and cleaning, as well as to be used for the removal of part 
of the contents of the boiler into the drainage system of the plant while 
at work, if this is desired. Such a pipe will be called the blow-off pipe 
and will have in it, and as close to the boiler as convenient, the blow-off 
cock or valve. From its location at the lowest and coolest point the 
solid matter, mud, and precipitated salts will gather in its neighborhood, 
so that when opened with pressure on the boiler a rapid rush of the hot 
water out through the valve and pipe will carry away sonde of the 
material of this sort. For this reason the blow-off valve is located in 
the mud-drum of boilers which have one. A gate or cock-valve is to be 
preferred for the blow-off valve, because it is not liable to become 
clogged from the precipitation of salts which may harden about it, and 
for this same reason also it is desirable that the pipe should be of generous 
size, so that it may easily free itself of the accumulations which may 
take place within it. It should rarely, even in a small boiler, be made 
less than 2 inches in diameter. In brick-set boilers, where the blow-off 



BOILER ACCESSORY APPARATUS 253 

pipe must pass through the combustion-chamber, it is particularly 
liable to become burned out by the overheating to which it is liable if 
scale gets into it. It is for this reason quite customary to cover it with 
some incombustible and non-conducting material in that part of its 
length where it is exposed to flame and hot gas (see Figs. 70, 74, 137, 140, 
148, 178, 183, 185, 188). 

In boilers using salt water the blow-off cock must also be used fre- 
quently in order to reduce the percentage of salty matter which is forced 
into the boiler with the feed-water, but cannot go out with steam. 
This opening of the blow-off valve is called blowing down, and permits 
the concentrated solution to be diluted by pumping in water to replace 
that which has blown to waste. Modern practice admits little or no 
salt water as such to the boilers, but distills sea water in separate appa- 
ratus and pumps the pure distillate into the boilers to replace what is 
lost in whistles, sirens and other non-condensing apparatus, and from 
leakage. Flash boilers should be blown off every night. In the open 
country or at sea, the blow-off pipe may be open to the air or to the 
drains, or to waste overboard. In cities it is not desirable to blow hot 
water into brick and cement sewers, and in many places a blow-off tank 
is specified by law or ordinance. This has sometimes and improperly 
been made a simple brick cistern. It is better to make it of cast iron or 
of quarter-inch steel plate. In good water districts where blowing out 
or down is not frequent, its capacity may be as low as five per cent of 
the gross bulk of water in the boilers to blow into it : several tanks will 
be better than one large one in a large plant. The blow-off pipe comes 
in at the top of the closed tank, and the outflow from the top also 
reaches down to near the bottom. This makes a seal, so that the cold 
contents of the tank are forced out first before the new hot water comes. 
A vapor pipe from the top leading to the open air at the roof or at some 
height prevents pressure accumulating, or any siphon action. 

154. Loss in Blowing off. The loss from blowing hot water from a boiler is 
found by the following: 

Weight evaporated X (total heat — feed heat) = x 
Weight blown out X (sensible heat — feed heat) = y 

Total = X + y 

— = loss in per cent by blowing down. 

X + y ^ ^ 

155. The Injector. If the water for the boiler is not forced into it 
by a pump (paragraf 147) the alternative apparatus is an injector. 
Its fundamental theory was first propounded by Giffard, and his name 
is often attached to all embodiments of the principle however far 
these may differ from his original. The injector differs from a feed- 



254 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



pump for this same purpose, because the latter is based upon easily 
understood principles of pressure and resistance, and a greater volume 
of steam displaces a less volume of water where the head of steam- 
pressure and the resistance-head of the water-cylinder are the same. 
The injector, on the other hand, depends upon a direct conversion of 
heat energy into dynamic energy, and by a process not so obvious or 
plain as in the case of the steam-pump. 

The injector may be defined as an appliance or apparatus whereby a 
jet of steam moving at a velocity due to its pressure is made to impinge 
upon a mass of cool water, to which it transfers its 
energy to such an extent that the combined jet of 
steam and water will overcome a resistance-head equal 
to or greater than the pressure which actuated the 
original jet of steam. That is, a jet of steam issuing 
from a boiler into an injector will pick up a quantity 
of water, and will be able to force that water into 
the boiler against the pressure which actuated the jet, 
and will carry the steam in the original jet also back 
into the boiler from which it started. 

The injector conforming to this definition consists 
of a hollow, somewhat tubular casting, • usually of 
brass, into which are made three openings. The first 
one {A, Fig. 240), which usually enters the top of the 
instrument, is for the delivery to it of hot, dry steam 
from the dome of the boiler or other convenient place. 
The second opening, B, is the inlet for the water to be 
fed, which is usually delivered to it from below. The 
third will be the feed-outlet, HI, opening towards 
the boiler, through which the feed-water impelled 
by the steam will pass to overcome the pressure on the check-valve 
and enter the boiler. 

The injector, properly so-called, has the cross-section of its tube pro- 
portions diminishing from the nozzle of the jet, in order that the velocity 
of the stream may increase from the point of meeting the water until the 
current streams into the vessel in which a high tension is maintained. 
If, on the other hand, the tube proportions are arranged to flare or 
increase in cross-section beyond the combining point, the velocity of 
flow is decreased, less resistance-head will be overcome, and the instru- 
ment becomes properly designated an ejector. The term injector may 
therefore properly be limited to instruments operating to force water 
against considerable resistances and in comparatively small volumes, 
the water becoming considerably raised in temperature in the process. 




Fig. 240. 



BOILER ACCESSORY APPARATUS 255 

The ejector, on the other hand, is adapted for handhng large volumes 
against low resistances, and by virtue of the greater mass of water 
handled the latter becomes only slightly warmed. Both injector and 
ejector as appliances for moving water are wasteful of heat as com- 
pared with a good pump; when apphed as a boiler-feeding apphance 
where heating of the feed-water is convenient and desirable, the in- 
jector does what can only be done with a pump by adding to the 
latter much of complication in the way of heat-saving devices. 

The injector depends on three sets of principles. Two of these are 
physical or mechanical, attaching to it because it is a jet and impact 
apparatus; the third are the thermal or heat principles, resulting from 
the heat-transfers when steam and water are the fluids concerned. 

156. Mechanical Principles underlying the Injector. The Induced- 
current Principle. The injector must be capable of lifting the water 
which it is to feed into the boiler from a level in a tank lower than the 
instrument itself. If circumstances permit the water to flow to it from 
a higher level, it does not require to use this capacity, and will be called 
a non-lifting injector. Where the machine must raise the water to its 
level it will be called a lifting injector. 

The principle on which the injector depends for its capacity to lift 
water is known in pneumatics or hydraulics as the principle of induced 
currents. If a jet of steam or air or water is made to move with a 
considerable velocity in a line parallel to the axis of a second or larger 
tube which surrounds the issuing jet, the impact of the matter issuing 
from the moving jet upon the matter within the surrounding tube will 
cause the contents of the latter to move with the jet in its direction. 
The action may be an impact of particles, or it may be a frictional 
entrainment of the one fluid by the movement of the other. If the 
cross-section or profile of the inner jet and the outer tube be adjusted 
to each other in the light of experience, the jet will induce a continued 
flow, tending to exhaust the contents in the space in the outer tube B 
which lies behind the orifice of the inducing jet C. This principle is a 
familiar one in the exhaust-steam blast in the locomotive, in the atomizer 
of the chemist and physician, and in many much-used applications. 
As applied in the lifting-injector it requires that the space behind the 
nozzle of the operative jet be connected by an air-tight pipe to the suc- 
tion-tank, within which it must be so immersed as to be water-sealed. 
In front of the nozzle of the jet must be an orifice opening to the air or 
to some waste-connection. With this latter orifice open, if the operating- 
jet be started, it will carry with it the air behind the jet until the pressure 
between the jet and the suction-tank becomes so much less than the 
pressure of the free atmosphere that the latter forces water up the 



256 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

suction-pipe to maintain the equilibrium. If the suction-pipe be not 
too long — probably less than 20 feet of the possible 32 feet — and the 
water in the suction-pipe is not so warm as to form a vapor in it under 
the reduced pressure, the induced current of air will cause the water to 
rise and meet the impact of the steam at the issue from the nozzle. 

The second mechanical principle is the principle of impact of a small 
mass of steam in the jet against the greater mass of the water which 
the induced current has lifted. This will be discussed in a succeeding 
paragraf. 

157. Heat-transfer, Work, and Efficiency in the Injector. The 
injector problem usually comes in the form that a certain weight of 
water W^ is to be forced into the boiler, and to do this work a weight 
of steam W^ must be expended. The weight of water will have its 
temperature raised from T^, which it had in the tank, to the temperature 
T2, which will be the temperature of the hot feed-water after leaving 
the injector, or W^ (^2 ~ ^4)- The weight of steam condensed by this 
weight of water loses an amount of heat per pound which is represented 
by the equation 

L== C{T,-T,) +xr, 

in which the specific heat may be called unity, and the percentage of 
vaporized steam is 100, or x equals unity, and r is the heat of vaporiza- 
tion at the temperature T^ in the boiler, at which temperature the 
steam enters the injector. For a weight of steam W^ this becomes 

WJi = W,[(T,-T,) + r]. 

The heat given by the steam must equal that absorbed by the water; or 

W^{T,-T,)^WA{T,-T,)+rl 

whence 



in ordinary temperatures, since differences alone are used. The tem- 
perature ^2 of the water in the pipe leaving the injector must be low 
enough to have the condensation complete, and yet the hotter it is the 
better so far as the boiler is concerned. It is likely to be about 160° 
with small or Hght feeding and 120° to 140° with heavier feeding. 
According as the upper or lower values are taken, a calculation within 
ordinary ranges of pressures will bring a relation of steam weight to 
weight of water ranging between 10 and 13. That is, the steam 



1 



BOILER ACCESSORY APPARATUS 257 

supplies from 10 to 13 times its weight of water. In the absence of 
tables for r, it may be calculated from the formula 



hT^ = 1114.4-0.7 T 



The water and the steam unite and flow together through the feed-pipe. 
The work to be done in the boiler where the water passes the check- 
valve will be the displacing per unit of time of a volume in cubic feet 
which is that of W^ + W^ pounds against the boiler-pressure. Since 
the pressure of the atmosphere is exerted within the injector {jPq), the 
effective pressure to be overcome at the boiler is p^ — p^. The volume 
of W^ -\- Wg in cubic feet will be 

"J/^ = 0-016 (TT^ + TTJ; 

hence the work will be, if pressures are in pounds per square inch, 

Work = 144 {Vi-Vo) X 0.016 {W^ + W,) foot-pounds. 
From this it is easy to pass to the efficiency, 



E = 



Work done 144 (p, - p,) X 0.016 {W^ + W,) 



Heat expanded 778 W,{T^-T^-\- xr) 

which as a rule works out a small value only. 

158. Mechanical Principle of Impact in the Injector. The mass of 
steam which meets the water in the combining tube of the injector has 
to act upon the latter by impact of the condensed water upon the feed- 
water. These masses being related to each other in a high ratio, such 
as one of steam to ten or sixteen of water, it follows that the principle 
of the conservation of the motion of the center of gravity will bring 
about a resultant velocity when they meet which will be to the velocity 
of the steam as W^ is to W^. That is, if the mass of the steam be one 
and that of the water be ten, then the center of gravity of the two 
bodies will lie nearest the water and at one-eleventh of the distance 
separating them, and the velocity of the combination after impact will 
be one-eleventh of that of the steam. If the ratio of masses be 15, then 
the resultant velocity will be yg- of that of the steam. 

The accepted formulae for the velocity of flow of a perfect gas from a 
reservoir within which is a pressure j)^ into another chamber where the 
pressure p^ prevails are those of Joule and Thomson. When the weight 
of a unit of volume is denoted by w^ at the pressure p^ and the cooling 
during discharge is adiabatic, then 



— rrTy5['-l;]-'.4T-i-ei) 



fc -1 
k 



258 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

in which k will have the value appropriate for the observed adiabatic 
expansion of the gas in question. For steam it is 1.111 according to 
Rankine, and according to Zeuner the value 

k = 1.035 + 0.100 a:, 

in which x is the initial proportion of dry steam-gas. Solving, with 
the assumption that the steam is dry, 



V ^ 23.2687 y py h ~ (^) 1 • 

The velocity of the mixture of steam and water will be less than the 
one-tenth or one-sixteenth of the foregoing values, because the impact 
of all particles cannot be in the line of propulsion. Calling this water 
velocity V2, the cross-section of the water-tube inside the injector 
will be 

0.016 {W^ + W,) 



Tube area 






The area of the steam-nozzle should be 

Volume of steam corresponding to W„ per sec. 
Nozzle area = ? 

from which the diameters will follow, since the area will be Tir^. 

It will be found, on making the calculation for any case, that the 
expenditure of heat-units resulting from the condensation process is 
so much greater than the equivalent expenditure in lifting the water 
by suction and of forcing it into the boiler, that these latter quantities 
are negligible by comparison. 

159. Double-tube Injector. The Inspirator. — The necessity of 
adjusting the weight of water to the weight of steam in the jet, and 
the variation in the latter with varying steam pressure brought about the 
self-adjusting types of injector, where the combining tube was moved 
forward or backward, enlarging or constricting the water-area as the 
pressure outside of the tube might vary. This was a feature of improve- 
ments by Sellers & Co. as far back as 1865 (Fig. 241). In 1876-7 
Korting of Hanover, Germany (Fig. 242) and Hancock of Boston 
introduced the use of two jets of steam to secure this same result. 
The first nozzle is the smaller and acts upon a relatively large mass 
of water to deliver it under a slight pressure to the second or larger 
steam-nozzle, which forces the supply to the boiler. The first jet 
will be the lifting-jet when the injector requires to raise its water. 



BOILER ACCESSORY APPARATUS 



259 



Inspirator was the proprietary name given by Hancock to his double- 
tube design. 

160. Restarting or Automatic Injectors. — An injector which will 
establish its action as a boiler-feeder automatically after the continuity 
of the combined jet has been broken by a stoppage of either the steam 




Fig. 241. 



or water-supply is called an automatic or restarting injector. The 
usual method of securing it is to have two steam-jets, one for lifting 
and one for forcing. When the continuity of the combined jet is 
broken by a failure of the water-supply, the discharge of steam from 




Fig. 242. 



the forcing-jet finds its way to a waste-pipe through a check- valve, 
while the lifting-jet keeps up maintaining a vacuum in the feed-pipe 
and draws up the water as soon as it can be suppHed. The adjustment 
of tubes and nozzles is also so made as to favor a wide variation of 



260 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

steam-pressures before a break in the flow shall occur. The advantage 
of the restarting principle is the simplification of the apparatus by 
doing away with adjusting spindles and the like, so that a simple 
valve on the steam-pipe to the injector is all the regulating appliance 
required. 

161. Exhaust-steam Injectors. The steam-current for an injector 
may be derived from exhaust-steam when the back pressure head is 
less than 75 pounds. The feed-water should flow to the apparatus 
and should be as cool as possible — never over 100° F. If a sup- 
plemental live-steam jet be added to revivify the exhaust-jet, the 
injector will feed up to 150 pounds. 

163. Advantages of the Injector. The advantages to be claimed 
for the injector are: 

1. From its construction, it is cheap. 

2. It is compact, and takes little space in proportion to its capacity 
for moving water. 

3. It has few or no moving parts, and hence a small running cost 
for repairs. 

4. It delivers the water warm to the boiler. 

5. It has no exhaust-steam to dispose of. 

163. Disadvantages of the Injector. The disadvantages . of the 
injector are those which belong to the apparatus as a class, and those 
which belong to certain forms of the instrument only. 

' 1. The impact of the jet on the water is not an effective method 
of pumping. As a pumping appliance the injector is about J as 
efficient as the equivalent steam-pump. Its duty is about 2 million 
foot-pounds, against 10 milfion for the pump. 

2. It heats its water with live steam, while to utilize the heat of its 
exhaust a pump with feed-water heater should show a superior coal 
economy of 12 per cent from the saving of waste heat. 

3. The feed-water must be cool enough to condense the steam-jet, 
and this limit is about 100° F. Hence the injector cannot be used upon 
hot water. 

4. It will not start with pressures much lower than those for which 
it was designed. 

5. If it is not a restarting instrument, it will stop working after 
the limit of co-relation of feed-water and steam are passed. Then it 
must be started anew by the operator. Often when it has become 
hot by the interruption of the water-jet, it can only be restarted by 
complete cooling with water. 

164. Water-gauges. Since the water rate or steam consumption 
of the engine is varying from minute to minute, and the pump rate 



1 



BOILER ACCESSORY APPARATUS 261 

can neither be constant nor uniformly varying, a piece of apparatus 
should be supplied such that the operator in charge can see whether 
the water is being supplied to it at the same rate that steam is being 
withdrawn from it, and regulate the supply of feed-water accordingly. 

A 'secondary use of the water-gauge device will be to enable the 
attendant to see whether the quantity of water, or the level of water, 
in the boiler is falling so low as to expose heating surfaces to the action 
of gas or flame without water on the other side, and also whether the 
water-level is rising to a point at which the priming or mechanical 
entrainment of water would be feared. The danger from low water- 
level in the boiler, whereby overheating is caused, would be that any 
or all of three injuries would follow. First, a general overheating 
would cause a corrosion or wasting of the iron by oxidation. Second, 
if there were any lack of homogeneity in the plate from cinder or 
defective welds, a blister would be caused (Fig. 26); and third, when 
the overheated plate was cooled suddenly by filhng the boiler with 
cool water the reduction of temperature would cause a sudden shrinking 
which, if not general and easily yielded to, might strain some joint of the 
boiler beyond its point of resistance when the boiler was already under 
considerable strain from the internal pressure. It is this last danger 
which makes low water so often a contributing cause to a boiler- 
disaster (paragrafs 191-208). 

165. The Glass Water-gauge and Water-column. The simplest 
form of water-gauge is a glass tube about a foot long or a little over, 
which is connected by proper fittings so that its bottom shall be 
below the lowest water-line, and its top above the highest (Fig. 243). 
These fittings are screwed into the head of the boiler directly in boilers 
which are not set in brick, and the water will stand in the glass tube 
at the same height that it stands behind the head of the boiler. A 
simple inspection by eye is all that is necessary to see whether the 
water-line is above or below the normal. In boilers set in brick, where 
the head is not exposed, the gauge-glass will be carried upon an inde- 
pendent vessel which will be connected by proper pipes above and 
below the water-fine respectively. This fixture is called a water-column 
(Fig. 244), and the water in it should stand at the same level as that 
in the boiler, and therefore make the gauge-glass show the water-level 
in all three vessels. Care must be taken in connecting the water- 
column that it shall be easily cleansed of deposit or other material 
which might clog it, and prevent its giving the same indications of 
level as are correct for the boiler itself. The connections shown in 
Fig. 244 will also illustrate those used for the high and low-water alarm 
columns (see paragraf 168), which are required by law as fixtures 



262 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




TOP OF UPPER 

oworYuB'K. 



OWATER SPACE 
OF BOILER. I 



&1RC0CK>: 




Fig. 



Fig. 244. 



BOILER ACCESSORY APPARATUS 



263 



for boilers in some of the states, using either floats or fusible allo}^ 
disks to operate the alarm function (paragraf 168). 

The advantages of the gauge-glass are its simplicity, its cheapness, 
and that it is easily observed. 

The objections to it are 

(1) Its fragility. It may be broken by accidental blows in spite of 
the brass- wire guards ml shown in Fig. 243 to prevent this accident. 




Furthermore, it is liable to break from a defective alignment of the 
two fixtures cramping the glass and causing it to crack, and also from 
a deterioration which the glass undergoes in service, particularly with 



264 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

waters containing any alkali. In locomotive practice the jarring 
tends to break the glass, and in confined spaces it is specially liable to 
accidental injury. When the glass breaks under pressure it will be 
apparent that two very powerful jets of hot water in one direction 





Fig. 246. 



Fig. 247. 



and of steam in another are thrown out from the fixtures, and under 
high pressure will fill the room instantly with hot and irrespirable steam. 
To prevent this difficulty a form of gauge-glass fixture has been devised 
in which the two attachments have an automatic valve opening inwards, 
and held in that position by a spring (Fig. 245) or by gravity (Figs. 246, 
247). When there is equal pressure on both sides of the valve the 
opening is clear into the glass-tube. When the tube breaks, the out- 
rush of steam and water will close the valves against the spring or 
gravity and thus automatically shut off the broken tube. Fig. 246 
shows this device with a ball as the valve to be closed when breakage 



BOILER ACCESSORY APPARATUS 



265 



occurs. The pin on the end of the spindle of the hand-valve (Fig. 245) 
forces the automatic valve away and opens the connection through 
the glass when the spindle is withdrawn. The spindle should be 
withdrawn slowly, so that the pressure may equalize in the tube with- 
out' drawing the valve to its seat. In Fig. 247 the valve is of the flap- 
type and while the chain pulls open the valve, the latter closes by 
itself. 

(2) The gauge-glass may give false indications. This may happen 
because the somewhat tortuous passage in the lower fixture has become 
stopped with scale. This can be guarded against 
only by frequent opening of the blow-cock at the 
bottom of the fixture, so as to wash it out and be 
sure that the passage to it is free. The indication 
may be deceptive because the lower valve is closed, 
preventing the water from descending in the glass 
when it descends in the boiler. This is best guarded 
against by making the valves of the fixtures to be 
cocks operated with a handle whose position indi- 
cates whether the valve is open or closed (Figs. 
246, 248). The third objection is the invisibiUty 
of the water in the glass when the water is clean. 
This can be obviated by having a colored strip made 
in the glass at the back which will be visible 
through the steam above the water, but which 
will be made invisible by diffraction caused by the 
water within the glass. The water usually is 
slightly colored, and it can be detected with care 
even if it is clean. The freedom of the connec- 
tions between the gauge-glass and the boiler can 
also be insured when the boiler is steaming by 
observing the motion which the operation of steam- 
ing always causes in the water in the boiler from 
the presence of waves. Fig. 244 shows a standard 
water-column with the connections for cleansing at the bottom. 

An Austrian invention known as the Klinger gauge-glass uses a 
flat, thick glass of trapezoidal section held in a brass frame. The 
back-plate behind the glass is fluted and at such angles for the sides 
of the ridges that when the water is in the space between the two the 
refraction which it causes sends the rays of light at such an angle that 
they do not reach the eye from the part where the water is. From the 
upper part the light is normally reflected (Fig. 248.) Hence where 
the water is appears black, while the back plate shows bright above 




Fig. 248. 



266 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

the water. Breakage is a cracking at most and does little harm but 
the chain shut-offs enable the gauge to be promptly isolated from 
pressure. 

166. The Gauge-cocks. By reason of the difficulties attaching to 
the gauge-glass, another form of water-gauge is usual without the 
glass or in addition to it. This involves the making of three or four 
openings into the boiler whi'ch can be opened by valves, and through 
which openings a sample can be taken from the level into which the 
openings are made. Such valves are called gauge-cocks or try-cocks, 
and will be fastened by screwing into the head of the internally-fired 
boiler, or into the column-pipe of the brick-set boiler. It will be 
apparent from Fig. 244 that if there are three of these cocks, the middle 
one should be at the normal water-level, the upper one above it, and the 
lower one below it. If the cock be opened above the water-line, it 
will permit dry steam to flow out, and its quality will be revealed to the 
eye and to the ear. The passage through the small opening will tend to 
superheat the steam, so that it will be an invisible gas for an inch or 
two from the nozzle, and will give a sound like the escape of a true gas. 
From the lowest cock water will be drawn, if it is below the water-level, 
but this water on reaching atmospheric pressure at the outlet will at once 
become saturated steam, which will be a white cloud from the very 
outlet of the valve, and will reveal itself to the ear by the difference in 
sound of the escape of water as compared with the sound of escaping 
gas or air. The middle cock, when the water-level is practically oppo- 
site its opening, will withdraw both steam and water, which will make 
the characteristic sputtering noise of air and water escaping through 
an outlet. The appearance to the eye will be the same as from the 
lower cock, since the water is the visible thing. Large boilers often 
have four cocks. 

These gauge-cocks require to be opened by hand and therefore must 
be modified for boilers whose water-level is higher than convenient 
reach. Different forms of try-cocks have been introduced, operating 
either by a weight which has to be lifted to open them, or else they 
are made like cock-valves which can be easily turned by an exten- 
sion which comes down to convenient reach. Figs. 244, 249, and 250 
show types of gauge-cocks. 

167. Float Water-gauges. — It has been sought for many years to 
find a satisfactory method of indicating the water-level by means of 
floats within the boiler whose position should cause the motion of a 
convenient indicator without. Some very early boilers had water- 
gauges of this class. The objection to them is the friction, which is a 
variable quantity and which acts upon the means used to transmit 



I 



BOILER ACCESSORY APPARATUS 



267 




Fig. 249. 





Fig. 250. 



268 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



the motion of the float inside to the indicator outside the boiler. 
The float is apt to catch and be held by such friction, and to fail to 
indicate the real changes in water-level. The other difficulty is that 
no float material has been found which does not ultimately become 
affected by heat and pressure/so as to absorb water from the water 
in which it stands and to become either partly or entirely filled. It 
seems to be a general idea that it is not safe to put sole dependence 
upon float-gauges for these reasons. 

168. Low-water Alarms. — It is quite possible, however, to use 
the float as a means of giving warning that the level in the boiler has 
been allowed to fall too low. This use is justified from the fact that 
they are not depended on, or should not be, for the normal working of 
the boiler, but are present 

as a safeguard if they fulfill 
their purpose in emergency. 
The usual plan is to allow 
these floats to control a 
valve where steam shall be 
admitted to a whistle. The 
normal rise and fall of the 
float within the limits of safe 
working is without effect on 
the whistle- valve, but it 
opens it if the float is too 
high or too low (Fig. 251). 
A similar device can be 
arranged, depending on the 
difference of expansion of 
metals in steam or in water. 
When a spindle is sur- 
rounded with water it is 
short enough to hold a valve 

shut, but when the water falls below the opening into the tube within 
which that spindle stands, the expansion of the spindle will open thevalve. 

169. Fusible or Safety Plugs. — As an additional safeguard to prevent 
injury from low water it has been the custom of many engineers and 
of some state legislation to demand that a plug shall be inserted into 
the boiler, at o'r near the dangerous low-water line, made of Banca 
tin or of some of the cadmium alloys, which have a relatively low 
fusing-point. When the disk or plug of siich fusible metal is covered 
with water the heat is transferred so rapidly that it should not melt. 
When the water leaves the plug, the lowered specific heat of steam 




Fig. 251. 



BOILER ACCESSORY APPARATUS 



269 



prevents the rapid withdrawal of heat, whereupon the plug melts, 
and steam blows out through the opening to give warning of trouble. 
Fig. .252 shows a construction of such fusible plug in which a brass 
shell is fitted with a core or disk of fusible metal. The objection to 
such 'fusible plugs is, first, that the melting-point of most of these 
alloys changes with time and is not always certain. Secondly, when 
covered with a crust of boiler-scale they may not be properly cooled 
by the water, and will fuse when everything in the boiler is normal. On 
the other hand, they sometimes fail to act, either from the first difficulty 
or from some unknown cause, and in 
any event, when blown out, it is 
annoying to replace them. The loca- 
tion of such fusible plug in a tubular 
boiler is shown in Fig. 178. 

The fusible-plug alloy has been 
applied as a safety or low-water 
alarm by inserting a disk or diaphragm 
of metal of this fusible quality in a 
pipe which admits steam to an alarm- 
whistle. When the pipe is sealed by 
the boiler-water, the plug does not 
become hot enough to melt. When 
the fall of the water-level permits the 

water to flow out of the tube, steam replaces it and has a sufficient 
temperature to melt the plug and blow the whistle. 

170. Automatic Feeding Apparatus. It has long been sought to 
arrange a mechanism which should be operated automatically, and 
as the level of the water in the boiler might vary, to have this change 
of level operate the feeding mechanism without human intervention. 
If automatic feeding in a reliable form could be combined with auto- 
matic stoking, the labor of the fire-room would cease to be manual 
and become supervisory only. 

It has been sought to obtain automatic feeding by several methods. 
They all make use of the direct-acting pump, and provide that the 
variation in water-level shall operate its steam-valve, so that the rise 
of the water-level above the normal shall shut off the pump, and a 
fall below shall turn on more steam and speed it up. This has been 
secured, first, by the expedient of having the steam-valve operated by 
the pressure of a column of water against a flexible diaphragm. When 
the water-level was normal, or above it, the bottom of this column of 
water was sealed in the water and thus kept full by the steam-pressure. 
When the water fell below its opening into the water-space of the boiler. 




270 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

the column emptied its water into the boiler, and thus withdrew its 
pressure from the diaphragm, which yielded to an exterior weight and 
opened the valve. A second method has been to insert in a pipe a 
rod of some metal with a high coefficient of expansion. When the 
outlet from this pipe into the boiler was below the water-line, water 
was forced up into the tube, and its high specific heat and radiation 
kept the rod cool. When the pipe was emptied by the fall of the 
water-level in the boiler, steam replaced the water around the rod, 
caused it to lengthen, and turned on the valve. A third plan has been 
by means of floats whose rise and fall within the boiler transmitted 
motion outside through a proper stuffing-box to slow down or start 
up the pump. The newer and better form of this to avoid the stuffing- 
box and its uncertainties of resistance, is to inclose the whole appara- 
tus in a casing, and have a float open and close a valve leading to the 
controlling piston or diaphragm (Fig. 251). This piston operates 
the pump valve. When the water rises in the column and lifts the 
float, the pin valve is opened and the spring is overcome and the pump 
slows down. When the float falls, the pin valve closes, the spring 
forces steam in the connecting pipe out through the bleeding valve 
and the pump speeds up. But the piston must never stick. A fourth 
plan, which has been used since the development of the electric motor 
for pumping, has been to make the rise and fall of the water-level 
operate a float to throw out or in a switch or a resistance-coil, in the 
circuit driving the pump, whereby the action or speed of the pump 
should be made to vary. 

The fifth method has been to have the feed-pump operating con- 
tinuously, and to arrange that its suction should draw from the supply 
of fresh feed-water only when the water-level was below a certain point, 
determined as before by the seal of a pipe by the water in the boiler. 
When the water was above the opening of the sealed pipe the pump 
simply circulated the boiler-water without drawing in a fresh supply. 
A modification of this principle used in flash boilers (paragraf 100) 
is to have the pressure in the boiler act upon a flexible diaphragm 
controUing a valve in the pump discharge. A spring resists the steam 
pressure, and when the pressure exceeds the determined point the 
feed is by-passed into the suction. This must work in connection 
with automatic control of fire-temperature, so that too little water 
shall cause excessive superheat and shut down the fuel supply, while 
a slight excess of water causing excess of pressure energy shall operate 
the by-pass and prevent flooding. 

The idea of an automatic or magazine feed-pump is a very old one, 
and will be found appUed to early boilers (Fig. 697 A in Appendix), 



BOILER ACCESSORY APPARATUS 271 

for which the feed was supplied from an elevated reservoir at such a 
height that the light pressure within the boiler could not balance the 
water-column, but water would flow in when a valve was lifted by the 
descent of the water in the boiler through the operation of a float. 

The objection to the automatic-feed principle as thus far applied 
has been that it is not entirely to be depended upon, or is not automatic 
in the true sense. The apparatus will work satisfactorily for six 
months or a year, and then, failing suddenly, causes a disaster or 
compels such repairs to the plant as to be a serious offset to the previous 
advantage. 

171. The Steam-gauge. It is entirely possible to operate a low-pres- 
sure boiler without an apparatus to indicate the pressure in it. Boilers 
were so operated before gauges in their modern form were cheap and 
portable. The relief valve (paragrafs 174, 377) could be relied on to 
open if the pressure went too high; the engine slowed down if the pres- 
sure fell too low. But this is neither safe nor economical with high 
pressures; it is not economical because it is important that the fireman 
in charge of a boiler should know whether the fire is supplying heat- 
energy to the water faster than it is being withdrawn in the form of 
steam, or slower, or just at the proper rate. The most convenient indi- 
cations of the heat-reactions are given by an appliance which shall record 
the pressure in the boiler, since if the pressure is rising, heat is being 
stored by the water, and if the pressure is falhng, heat is being given off 
faster than it is being supplied. Such an apparatus, therefore, becomes 
a reliable guide to the firing process. If the pressure is stationary, the 
water-feed, draft and heat supply from fuel are rightly related to each 
other; if the pressure is rising the rate of combustion controlled by the 
draft needs lowering, or this is the time to pump in an extra cooling 
feed supply; if the pressure is falling, the draft needs stimulating and 
perhaps the feed-pump may be putting in more cold water than the 
boiler can digest with the fire in that condition. In locomotives or 
motoi." vehicles, the steam-gauge is full of information as to whether 
with that load on that grade with that condition of track or roadway 
the speed then in use can be maintained, or can be increased or must 
be reduced. This strictly and properly is the principal function of 
the steam-gauge. A secondary but sometimes very important func- 
tion is to indicate whether the pressure and the heat-supply are rising 
so rapidly as to endanger the structure from excess of internal pressure. 

The first and simplest form of steam-gauge was a U tube or mano- 
meter. The size which this apphance has to receive with high pressure 
precludes its use as a pressure-gauge, although it remains the standard 
for all of its more convenient substitutes. It has been found most 



272 MECHANICAL ENGINFERING OF STEAM POWER PLANTS 

convenient to replace the weight of the mercury-column by a spring 
which shall undergo a known deformation for each pressure, and which 
shall indicate its deformation by the movement of a needle over a dial. 
Such spring may either be a flat disk or diaphragm, Fig. 253, or it may 
be a hollow brass or steel tube which is bent into an arc of a circle, and 
the sides permitted to come together by this bending, so that the 




Fig. 253. 



section of the tube is that of a very much flattened oval. When'pres- 
sure is admitted on the inside of this tube the parallel sides tend to 
separate, and in separating they must increase the radius of curva- 
ture with which the tube was bent within the circle. The tendency to 
straighten out by internal pressure can be indicated by a multiply- 
ing gearing which shall cause an indicating-needle to traverse an arc. 
Fig. 254 shows the ordinary Bourdon gauge with flattened tube avail- 
ing of this principle. Pressures below that of the atmosphere can be 
observed by similar appliances. The aneroid barometer is a vacuum- 
gauge. 

Fig. 255 shows a form of Bourdon spring in which the two arms have 
been shortened so as to prevent their shaking disagreeably when exposed 
to the jarring in locomotive service. Sensitiveness or a considerable 
motion of the needle is secured by a double connection to the multiplying 
device. This arrangement is also of advantage for use in gauges which 



.j 



BOILER ACCESSORY APPARATUS 



273 



are to be exposed in portable boilers to temperatures below freezing. 
The two arms can be drained of the water which they will contain from 
condensation, whereas the form of Fig. 254 will always hold the water 





Fig. 254. 

which has once entered it. It is usual to secure the separation of hot 
steam from the gauge-spring by an intervening water-column, for which 
provision is made by connecting the gauge to the boiler through a 





Fig. 255. 



U tube, which will make a siphon (Fig. 244). Fig. 256 shows a device 
which produces the same effect as a water-seal. Provision, however, 
should be made for draining this siphon both for cleansing indoors and 
to prevent freezing without. 




274 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

The defects of such spring-gauges are: 

(1) The spring loses its original resilience by use and heat. If this 
is due to a permanent change in the structure of the material, the 
gauge is useless. 

(2) Rust and improper treatment may cause the friction of the needle 

mechanism to prevent the recording of the full pressure 
against the spring. 

(3) The needle may slip so as to change its relation to 
the spring, which will cause the gauge to record per- 
manently above or below its proper pressure. 

172. Standardizing or Calibration of Steam-gauges. To 
ascertain the accuracy of a gauge it is to be compared with 
a standard. It is usual to compare it in practice with a 
test-gauge, which is one kept specially for this purpose and 
Fig. 256. not exposed to the conditions of service. The test-gauge, 
however, requires to be itself standardized, and for this pur- 
pose three methods are usual. The first is to connect the gauge which 
is to be tested upon a pipe or similar apparatus within which hydraulic 
pressure can be admitted to come also upon a valve closing an opening 
which is made exactly one square inch of area. By loading this valve 
with known weights, and observing the pressure recorded by the gauge 
when the water-pressure Hfts the valve and weights, the gauge is cali- 
brated. This can also be done with a piston which can be loaded with 
known weights moving without friction, or with a minimum friction, in 
a cylinder. 

The ultimate standard is the mercury-column. The gauge to be 
tested is connected on the same pipe which opens into the short leg of 
the mercury-column, and the pressure recorded in the gauge when the 
mercury in the long leg stands at the heights which correspond to the 
real pressure indicates its error or its truth. 

173. Recording-gauges. It is convenient to have a continuous 
record of the variations of pressure in the boiler or in the other appH- 
ances in which pressure is to be observed. It is very simple to connect 
the spring or piston mechanism of the gauge or testing appliance to a 
link carrying a pencil-point which shall move in one direction by varia- 
tion of pressure over a piece of paper which is made to travel in a direction 
at right angles at a known rate by means of a clock. The pencil-point 
traces a line as the pressure directs, and the intensity of that pressure is 
measured by the vertical ordinates on the diagram, while the time at 
which it occurred can be found by a horizontal measurement. The same 
result may be compactly attained by giving a radial motion to the 
recording pointer receiving pressure, while the card or receiving paper 



BOILER ACCESSORY APPARATUS 275 

moves circumferentially under it by a clock movement. Such records 
are not only a check upon the fireman's fidelity and competence, but are 
means of avoiding controversy as to responsibility where pressures are 
factors in the satisfactory operation of any plant. 

17*4. The Relief or Safety-valve. The steam boiler being a reservoir 
of heat energy in the form of pressure, it is plain that an attempt to 
store too much heat will produce such a stress in the material enveloping 
the steam and water as to exceed its resistance to rupture from such 
internal pressure. A relief valve opening outward and held shut by an 
adequate and adjusted force can easily serve to secure safety for the 
vessel by guarding against such accumulation of pressure energy. It 
does not necessarily secure safety unless some steps are at once taken to 
check the flow of heat and energy into the water; that is, a valve of this 
relief-type is not a safety-valve in the true sense, unless as it lifts it 
has sufficient area to allow all the steam to escape through the opening, 
which will be made as fast as the boiler can make steam with all other 
outlets closed. In other words, the pressure in the boiler should not be 
able to rise above that for which the valve is loaded, even if all other 
outlets are closed and the fire burning with its normal or even its maxi- 
mum capacity for steam-making. Comparatively few safety-valves 
are of this capacity, for reasons of cost and convenience, but the presence 
of such a loaded valve acts as an alarm to give warning of the passage 
of the known pressure-limit, so that means may be taken to stop the 
generation of steam and an accumulation of pressure. 

Furthermore, as the pressure does accumulate under the valve when 
open and blowing, it has a tendency to lift the valve higher and enlarge 
the outlet in many of its forms. Most of the legislative requirements 
concerning boilers compel a safety-valve of an accepted construction. 

175. Forms of Safety-valve. The safety-valve for boilers is likely 
to be in one of five forms. Historically the first, now practically not 
used in America, is the method of weighing the valve down by a direct 
weight, resting on its back or suspended to it from below (Figs. 96 and 
98). The difiiculty of this form is that with large valves and high 
pressures the weight to be used becomes considerable and inconvenient. 
In English practice, where the direct weight is still preferred, the 
inconvenience is mitigated by using a number of smaller valves to secure 
the necessary area and subdivide the weights. 

The second form is to replace the weight with a spring whose intensity 
can be graduated. This avoids the bulk of the direct weight, but is 
open to the serious objection that as the valve lifts the resistance of 
the spring increases. The springs are also hable to corrosion, which 
makes them stiff. This form was used in many cases where jar from 



276 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

motion was to be experienced, but has practically been entirely super- 
seded by the fifth form. 

The third is a very frequent type, in which the spindle of the valve 
is held downwards by the action of a lever carrying the resisting weight 
with a long arm, while the effort of the valve to overcome the weight 
has but a short lever-arm (Fig. 257). This does away with the 
inconvenience of a great weight, and makes adjustment of the pressure 




Fig. 257. 



to hold the valve shut both easy and rapid. It is probably the most 
widely prevalent form of safety-valve for stationary boilers. The 
objection to it is the tendency of the lever in its rise to cause the valve 
to become jammed from the oblique motion around the fulcrum of the 
lever. It may also be urged as an objection to it that the weight nmy 
be so easily increased by sliding out the regular weight or by hanging 
other weights upon the lever. It is also easy to stop the valve from 
operating by wedging it so that it cannot open under any pressure 
whatever. The lever-valve construction lends itself to a desired use 
in river-boat practice. By attaching a rope or chain to the end of the 
lever and leading it up over a pulley, with a weight on the free end, 
that weight acts negatively and takes weight off the valve, and lightens 
the pressure at which the valve will open when the engine is at rest. 
By hanging this second weight up so as to leave the rope or chain slack 
by which it is attached to the lever, the entire counterweight comes 
on the lever, and full pressure is restored for regular running. 

For locomotive use before the fifth form was introduced it was 
usual to replace the weight by a spring which acted at the end of a 
lever to hold the valve down. This spring was arranged so that the 
tension upon it could be varied by the engine-runner. It never became 
widely used outside of locomotive practice. 



BOILER ACCESSORY APPARATUS 



277 



The fifth form is what is called the pop or reaction safety-valve, 
which is practically universal in locomotive practice, and is widely ex- 
tended elsewhere. The principle of the pop-valve is that, as the valve 
proper lifts from pressure, the escaping steam, instead of passing out 
directly from under the valve, must find its way out, after undergoing a 
change of its direction in an annular groove formed in the valve outside 
of its inner bearing. The force due to the reaction of the steam in 
escaping adds an additional effort to 
lift the valve, increases the opening 
thereby, and with a given loading 
the valve will remain open until the 
pressure within the boiler has fallen 
perhaps 5 pounds below that at which 
the valve lifted. The additional area 
exposed to pressure when the valve 
lifts causes it to open with a sudden 
motion which has given it its ordinary 
name, and it also closes suddenly 
when the pressure has fallen. Figs. 
257 and 258 show types of lever and 
of pop safety-valve. 

A failure of the safety-valve is 
often due to corrosion either of the 
valve upon its seat or of the guid- 
ing-spindle in its guides. The safety- 
valve, therefore, should be frequently 
lifted by hand in order to be sure that 
corrosion has not made it worthless, 
and a further safeguard is secured 
by the use of metals in the valve or 
seat which do not rust together. 
Nickel has been applied for valve- 
seats with success by reason of its being a non-rusting metal, and 
certain bronze alloys are used for the same reason. 

176. Safety-valve Formulae. " Experiments on Flow of Steam," by R. D. 
Napier (see Engineer of London, September to December, 1869), gave for discharge 
from a conoidal nozzle per inch of area per second, provided the pressure into which 
steam flows is less than three-fifths of that in the boiler from which it flows, 

Vi 

^ = 70 ; 




Fig. 258. 



or, for an area of a square inches, 



70 



, 70iy 
whence a = 



278 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

in which w should be the entire weight of water which the heating-surface can 
evaporate in one second of time. Some other formulae for safety-valve areas are 



grate-area 
in sq. ft. 



rate of combustion in 
pounds per sq. ft. 



pounds of water "1 
evap. per pound I X 70 
of coal per hour J 



3600 P 
coal burned per hour 



5.14 P 
pound of coal); or 



(assuming that 10 lbs. of water are evaporated per 



p + 10 ' 

or A = 1 sq. in. to 25 sq. ft. H. S.; 
or A = 1 sq. in. to 1 sq. ft. G. S. 

The lift of a safety-valve is usually a very small quantity. The standard experi- 
ments on a conical seated valve four inches in diameter are those of Burg in Vienna. 
His values were, with a pressure below the valve of 

12 20 35 45 50 70 90 
the lift of the valve in inches was g^ ^^ 5^ -^^ /e jJs -^ 

The area of the opening is the cylinder or cone included between the valve and its 
seat when the valve is open. Its area will be the circumference of the valve multi- 
plied by the foregoing small lift. 

177. Computations for the Lever Safety-valve. The equation for a safety- 
valve of lever type is 

{Px A) xl =WL, 

in which A is the area in square inches; Pthe pressure on each square inch; TFthe 
weight in pounds on the long arm of the lever, and strictly should cover the weight 
of the lever-arm, applied at its center of gravity; L is the length in feet or inches 
from the fulcrum to the weight; and I i« the length in the same unit from the fulcrum 
to where the spindle of the valve presses up against the lever. The U. S. law com- 
pels I to be more than 4 inches, and L cannot be over 40 inches. 

178. Concluding Comment. In the foregoing chapters the power 
plant in its generating function or in the boiler-room has been con- 
sidered in its simplest and most uncomplicated form. Additional 
apparatus for increasing economy and lessening cost of production 
will be taken up in a later chapter under Boiler-room Auxiliaries. 
At this point the designer or seller or writer of the specifications for 
the plant turns it over to the buyer or owner or operator to be run. 
The problems facing such owner and operator will be discussed in the 
next chapters under the headings of care and management. 



CHAPTER XI. 

CARE AND MANAGEMENT OF BOILERS. 

180. The Firing. The firing of a boiler-furnace is to be done in 
accordance with the general principles of combustion, and the applica- 
tion of these to fuels which differ so widely makes it difficult to give 
anything but the most general suggestions. References also have 
been made in other connections which bear on this subject. The three 
usual methods of firing are the spreading method, the side-firing or 
alternate method, and the coking method. The spreading method is 
to keep covering the fresh and incandescent coal on the grate with 
thin layers of fresh coal thrown in at short intervals. This is the 
usual and most successful method with anthracite, where best results 
are secured when the fire is least disturbed. Side-firing is to divide 
the furnace into two halves lengthwise and charge the fresh fuel on one, 
while the other is in its best state of incandescence. This has been 
referred to under the double Cornish or Lancashire method as a means 
of keeping up the temperature of combustible gases, and is especially 
applicable to bituminous coal. The coking method is to divide the 
fire crosswise instead of lengthwise, and charge the fresh coal containing 
gas at this front part or on the dead-plate, and push it backwards when 
the gas has been distilled by the radiant heat of the fire behind it. 
The thickness of the fire will be determined by the draft and the 
quality and size of the fuel. Anthracite fires will be as a rule thinner 
than bituminous, and small coal will require a thinner fire than the 
larger sizes. With thin anthracite firing from 4 to 8 inches is accepted 
good practice, and with bituminous coal from 6 to 14 inches. 

The starting of fires in the boiler-furnace is also a matter which varies 
with the fuel and the conditions of draft. If the chimney is reluctant 
to draw from its being cold, it can be helped by starting a little wood- 
fire in the base of the stack and beyond the boiler-setting, so as to create 
the first action of the chimney before the resistance of the setting is 
interposed. It must be remembered that anthracite ignites reluctantly 
and large quantities of wood are necessary to get it well started. 

181. Cleaning Fires. The interval between cleaning of fires will 
depend on the rapidity of the combustion and the quality of the fuel 
with respect to ash. With anthracite fires it is usually only necessary 

279 



280 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

to clean fires in stationary practice about four times in twelve hours. 
With bituminous coal it must be done more frequently, and often the 
best results are obtained by pulling the fire about at short intervals, 
which is fatal to the satisfactory working of an anthracite fire. The 
cleaning is done by means of slice-bars which break up the clinker and 
separate the combustible from the incombustible matter, and after the 
fire is thoroughly broken up the aggregations of incombustible matter 
are removed by a rake or hoe. What remains is then spread evenly 
over the grates, and a fresh charge of fuel thrown on the fire. The ashes 
and clinker drawn out from the furnace will then be extinguished and 
cooled by a jet of water from a hose, and will then be removed. Care 
must be taken in handling the extinguishing water that it should not 
strike by accident any of the hot castings about the ash-pit, which it 
would be certain to crack. 

182. Banking Fires. It is usually the least trouble and expense to 
bank the fire at the close of the day, or when the fire is to be kept over 
for some hours during an interval of inaction. After the fire has been 
cleaned, what remains on the grates, instead of being spread evenly, is 
piled against the bridge-wall and upon the back half of the grates, leaving 
the front part bare. Fresh coal is then charged in a thick layer over 
the banked fuel, and the fire is left with the ash-pit doors closed, the 
fire-door open with anthracite fuel, but closed with bituminous, and the 
damper closed, or nearly so. The closure of the ash-pit and the access 
of cold air above the fire make the ignition of the bank of fresh coal very 
slow, so that several hours will elapse before it has become ignited, 
and even then it burns slowly and not actively. At the end of the time, 
determined by the quantity of fresh coal used in banking, the fire is 
cleaned and spread, and is ready for a new campaign. 

183. Regulation of the Fire and Pressure of Steam, The regulation 
of the fire is done by controlling the access of air to it whereby com- 
bustion is stimulated or checked. The closure of the ash-pit and the 
damper check the fire, and to open them stimulates it. The fire-door 
opening into the furnace above the grates is a further means of con- 
trolling the fire in part, since by opening it cool air comes in to lower the 
temperature in the fire-box, and without passing up through the coal 
it does not stimulate combustion. The cool air further checks the 
making of steam by cooling the products of combustion, and acts by 
contact as a cooling medium passing over the heating-surface and 
through the tubes. It has already been noticed that this is not a 
desirable thing to do, by reason of its effect on the metal of the boiler, 
but it is an efficient method of control. 

The steam-pressure is controlled by the fire principally, but it can 



CARE AND. MANAGEMENT OF BOILERS 



281 



also be regulated by the use of the feed-water. The introduction of 
cool water cools the contents of the boiler, and checks partly or alto- 
gether the formation . of steam. The presence of additional water, 
furthermore, makes additional material to absorb heat-units, so that 







Fig. 260. 



great skill is to be shown when known variations for demands for steam 
are to be expected, by so controlling the times for feeding and the 
amounts fed that this storage of heat shall be utilized to its best extent. 

184. Cleaning the Heating-surface outside. The metal of the heating- 
surface in most boilers becomes coated with a scale of some non-con- 



282 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

ducting character caused by the Hght dust and ashes attaching them- 
selves to the plate, and particularly when tarry matter is present in the 
products of combustion. Within the tubes of a tubular boiler a deposit 
of dust and ashes will also take place, perhaps choking the tubes, or at 
any rate rendering them less efficient (Fig. 8) . The cleansing of these 
exterior surfaces from the soft scale is done either with scrapers, or by 
brushes (Fig. 260), or by means of a jet of high-pressure steam or air 
directed upon the surface to be cleansed from a nozzle (Fig. 261). The 
tube brush or scraper is passed through the tube and scrapes the surface 
clean, but the steam-jet acting at high velocity seems to have a special 
cleaning effect, and is used either independently or in connection with 




Section view o£ 
nozzle. 



Fig. 261. 



the scrapers. Special forms of such steam-cleaners are used, in which 
the jet receives an annular form and a spiral motion (Fig. 261), but very 
good results are obtained by means of a simple short-length of pipe 
coupled to the steam-space in the boiler by means of a flexible hose. 
The settings of sectional boilers usually have openings made through 
their walls in which pipes are built, and through which pipes the cleansing 
jet of steam can be inserted at different levels, and so keep the surfaces 
up to their efficiency. The tarry deposit sometimes refuses to be moved 
by the steam-jet, when, of course, scrapers must be used. 

Locomotives are more often cleaned by air-jet, because of the danger 
to the person cleaning if any accident should occur to the hose joints 
while he is confined within the fire-box. With steam in use under these 
conditions, the cleaner would be burned before he could escape, while 
with compressed air there is no such danger. 

185. Boiler-scale or Incrustation. It will be apparent that any solid 
matter in solution or present in suspension in the water fed to a boiler 



CARE AND MANAGEMENT OF BOILERS 



283 











• o 




• OJ OS 




• o 

• CO 

• 00* 


















Rock- 
ford, 111. 
Artesian 

Well. 


CO ^ 
O 00 




■ CO 

• CO 

• CO 








lO CO 
lO CO 

• d d 


■ lO 

• d 




• d 








Downer's 

Grove, 

111. 

Well 

very Bad. 


-^ Oi CO 

t- o o 

O t^ ""^ 






















■ <N 

• d 








River- 
side, 111. 
Well. 


rj< t^ CO 
00 CO t^ 
■* (N t^ 

dio d 


• CO 

• (M 

• O 




















• CO 

d 








Missis- 
sippi 
River 
at Keo- 
kuk. 


O CO 




• in 

• 00 

d 






• 05 


o 

o 

d 


O 05 CSI 

CO oo oo 

Ttl -rt* CO 

d d (N 




O iO 
00 -* 


Missouri 

River at 

Council 

Bluffs. 


c^ i>. ^ 

<M '<:t< lO 

lO 00 C^ 

T-1 OO c<» 


CO lO 

CO o 

oo lO 

T-H CO 


















CO , 
CO 

d 








Missis- 
sippi 
River. 


CO O "* 
CO I>- oo 
00 OO "* 

d CO o 


CO oo 

O CO 
O CO 

'^' d 


















CO 
CO 

o 








Lake 
Michi- 
gan. 


o S o 
CO "* CO 

d ■* o 












uo 

d 


CO 
oo 

d 


05 

o 
d 










2 ij 


oo r- 

O 00 

d ^ 




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CO o 

d d 








d 










CO 

CO 

CO 






u 








d ■ 


d d 






CO 
CO 

o 
d 




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oo 

CO 

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d 


d d • 






6^ 




2^§g : 

CO CO -* CO • 

.-1 (M o o ■ 
(zi d <z> d ■ 








CO t^ 

oo »o 

CO 1-1 • 

d d • 










d \ 








6 


6 
o 

d 

a 

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d 

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4 

O 

a 

'c 

Is 

O 


O 
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Si 

a 

(D 

G 


d 

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p. 

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S 
cj 


g 

a 

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3 : 

q; 

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f 

c3 
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d 

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a 

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m 


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o 

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a 


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0) 
T3 
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<D 


3; 
+^ 

g 
O 

1 

bX 

O 

OJ 
T5 
G 





284 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

'v\dll remain behind in the boiler when the water is evaporated, because 
the steam will carry none of this material with it. If the salts in the 
water are of a soluble character, the process of evaporation will tend to 
concentrate the solution which remains in the boiler, and if they are 
insoluble they will gradually fill up the water-space. Concentration 
of soluble solutions is prevented by the process of blowing dqwn 
(paragraf 153), but for the removal of the insoluble matter some 
special procedures or appliances must be used. 

The solid matter which gives trouble inside of boilers is introduced 
either in suspension or in solution. When it is in suspension the water 
is called a muddy water, and the proper procedure is to filter the feed- 
water for the removal of such suspended matter. This gets rid of the 
difiiculty from this mud outside of the boiler altogether by preventing 
it from getting in. If this is inconvenient, the mud-drum will be a 
necessary feature of the boiler, and blowing off the accumulations must 
be practiced at frequent intervals. 

A class of saJts enters the boiler in solution, but is precipitated as an 
insoluble precipitate on boiling. These are among the most trouble- 
some, because they are really formed within the boiler itself, and con- 
sequently can only be prevented from getting in by chemical reactions 
of some magnitude. The salts of this class are the carbonates of the 
alkaline earths, lime and magnesia, and the sulphate of lime, which 
is the most troublesome of all. The feed-waters which are usually 
drawn from fresh-water sources are not likely to contain much sodium 
or potassium, which form the soluble salts, but in sea-water the chloride 
of sodium and magnesium, which are both soluble, are elements which 
give it its salty taste. Silica, alumina, and organic matter are to be 
found in some of the Western waters, or where the wash of surface-water 
may have come into the source. Typical water analyses from various 
sources are given in Table X. 

Great difference in the difficulty of the problem of dealing with boiler- 
scale results from the form which the scale takes. The carbonates of 
lime and magnesia are a mud — white or grayish in color when pure. 
They have no cementing tendency and can be treated like suspended 
impurities. Silica and the sulphate of lime, however, are crystallizing 
bodies in the water which form into a hard, adhesive crust, and not only 
this, but they have the property of causing the carbonate scales to 
crystallize with them and add to the extent and thickness of the 
adhesive coating. The following table shows the properties of these 
most prevalent scales, and their degree of solubility at various tem- 
peratures. They enter the boiler as the bicarbonate, which is soluble, 
but on boiling one part of carbonic acid is expelled, and the protocar- 



CARE AND MANAGEMENT OF BOILERS 



285 



bonate which remains is the insoluble form. The carbonate of magnesia 
is a light, flocculent powder which usually floats at or near the surface 
of the water, rather than sinks to the bottom. Organic matter is apt 
to act in the same way, especially when it is of a vegetable character. 



TABLE XI. 



Salt. 



CaCOg and MgCO- 

Do ! 

Do 

Do 

CaSO^ 

Do 

Do 



Temperature. 
Degrees Fahr. 



62 

212 

285 to 300 

62 

95 
212 
290 



Authority. 



Bucholz 

Do 
Couste 

B. 
Regnault 
R. & B. 

R. 



Parts by Weight of Ufi 
to dissolve 1 Pint of Salt. 



41,600 to 62,500 

16,0C0 to 24,000 

Insol. 

461 

393 

460 

Insol. 



Grains to 
Gallon. 



1.4 too. 9 

4.25 to 2.75 



126 

178 

126 





186. Inconveniences due to Boiler-scale. The presence of the sohd 
matter in the water of a boiler may do harm in one or more of four ways. 

(1) If it forms hard and solid over the heating-surface, it adds a non- 
conducting thickness to the evaporating-surfaces, so that an excess of 
fuel is burned to make the required quantity of steam. 

(2) This non-conducting covering causes the metal of the boiler to 
be overheated because the water does not cool it. This may produce 
an injury which is general or local. The general deterioration all over 
comes from an oxidation of the plate on the outside, because its high 
temperature makes the oxygen reactions more rapid than they would 
be if the plate were cool. The local injury comes from the presence of a 
thickness of scale at points exposed to intense action of fire, whereby 
they become practically red-hot and softened, so as to yield under the 
internal pressure. Bags or blisters result from this trouble, which is 
aggravated if grease has become mixed with the scale at the point in 
question (Fig. 26). A lump of scale is sometimes carried by circula- 
tion and dropped in a special place, and becoming attached there, a 
local overheating begins underneath it. 

(3) The scale which crystallizes, accumulating in feed-pipes, blow-off 
pipes, water-gauge connections, and the like, is occasion for trouble in 
the use of these appliances (Figs. 237 and 244). In sectional boilers, 
besides the annoyance from the first two causes, the presence of scale 
impedes the rapid circulation, and increases the troubles which are met 
from this difficulty (Chapter VI). 

(4) The presence of the floating mud or flocculent precipitate causes 
the boiler to prime, because the steam-bubbles must force their way 



286 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

through the scum at the disengaging-surface, and in doing so water 
follows upwards with the steam, and is entrained mechanically through 
the steam-pipe (paragraf 49). 

The ill effects or injuries caused by scale are to be mitigated or 
avoided by methods which can be grouped under three heads. The 
first is the removing of the scale which is allowed to form. The second 
is the preventing of the solidification of the scale either by changing its 
character or by other means, and then causing its removal by methods 
of the first class. The third is the purification of the feed-water from 
its impurities before it enters the boiler. 

187. Removal of Boiler-scale. When the scale is a mud and without 
tendency to cake upon the heating-surface : 

(1) The boiler can be allowed to cool down full of water, and when 
cooled emptied through the blow-off pipe. By removing the manhole 
and entering the boiler with hose-jet and brooms, the accumulations of 
soft scale can be washed out and the boiler is clean. 

(2) The mud can be prevented from accumulating and with an 
efficient mud-drum can be removed, by blowing the boiler down at short 
intervals during the day, and blowing it out completely at the end of a 
week or oftener. The objection to this method is that the scale which 
is not thoroughly washed out by the outflow through the blow-off pipe 
will dry on the heating-surfaces in a cake which it is difficult to remove 
when it has once solidified. 

When the scale is of the character which cakes on the metal of the 
boiler, due to the presence of sulphate of lime, two methods can be used : 

(1) The boiler being emptied of water and cooled empty, a brisk 
fresh fire is started under the empty boiler. The effect of this is to 
expand the iron at a rate faster than the scale, and causes the latter to 
crack off in flakes, which are then swept out after the boiler is cooled 
again. The objection to this is a fatal one, in that it is very hard on 
the boiler and injures it. 

(2) A more usual plan is to allow the boiler to cool, empty it, and enter 
it through the manhole with what is called a scale-pick. This is a 
species of hammer with both faces formed to a wedge, and with it the 
scale is struck and broken very much as a film of ice is broken off the 
exposed stones of dwellings or pavements in Northern cities. The 
objection to this method is that the forcible removal of scale carries 
with it the film of oxide of iron which is formed on the inside of a boiler, 
and which adheres to the scale rather than to the iron. The ultimate 
effect is to thin the iron by this continual removal of the oxide film. 

Belonging to this same class of methods is the use of an apparatus in 
the form of a trough or false bottom inserted within the boiler, and so 



CARE AND MANAGEMENT OF BOILERS 



287 



arranged as to catch the precipitate which is moving with the currents 
of circulation. When the soHd matter has fallen into such pan or 
trough it no longer is exposed to circulation, but lies where it has fallen, 
and therefore does not have a chance to get to the real heating-surfaces. 
This, of course, is a method available in shell boilers only. For the 
flocculent or floating type of scale a blow-off connection at the surface 
of the water in the boiler has been found convenient (Fig. 262). This 
has been arranged to have a trumpet-shaped mouthpiece whose ampli- 



Flattened Mouth piece 
extending across Boiler 




FiG. 262. 



tude is greater than the normal range of the water-line in blowing 
down, so that when the attached valve is open, surface-water flows 
into the trumpet mouth and out of the boiler, carrying with it the 
floating scum. In sectional boilers the main dependence against the 
adhesion of scale within the small units which make it up is the rapid 
circulation (see Chapter VI), but special cleansing tools have been 
devised to meet this problem, in which an appliance driven by steam 
or air can be introduced within the tube. It has cutting or impact 
tools which break up and loosen the scale so that it can fall out or be 
swept away. (Figs. 263 and 264). The impact will loosen some 
scales upon the outer surfaces of fire-tubes, but not all. They are 
mainly directed to work in water-tubes. 

188. Prevention of Scale-formation. There are three great methods 
which are used to prevent the scale from forming a hard, adhesive crust 
or coating. The first of these is to introduce in a boiler some reagent 
or material which shall prevent the scale from hardening or crystallizing 
by a sort of mechanical reaction. This is the basis of methods which 
have been used involving the introduction of sand, sawdust, malt- 
grains, and similar material which shall form the nuclei around which 
the scale is to sohdify in the form of balls or larger grains and remain 
in a form easily removable. 

The second method has been to make use of some material in the 
boiler which shall act as a varnish caked upon the surface of the boiler, 



288 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




so that the adhesion of scale shall be made more uncertain. The 
introduction of kerosene, starch, or the real varnishing of the surface 

with some suitable composi- 
tion all operate in this way. 
Perhaps kerosene is one of the 
best known of the, reagents 
of this class, and for many 
waters seems to be the best 
to be used in this way. It is 
introduced either gradually 
b}' a small connection to the 
feed-pipe suction, or a charge 
is put in at intervals. Mineral 
oil or grease does not meet the 
case, by reason of the ten- 
denc}^ which it has to adhere 
itself to the heating-surface, 
and, by keeping water from 
contact with the metal, to 
cause overheating as badly as 
the scale itself, if not* worse. 

The third method is to in- 
troduce a reagent which shall 
act chemically on the pre- 
cipitate either to change its 
crystalKzing or solidifying 
character, or to change an 
insoluble into a soluble salt. 
The reagent may be either 
an acid or a salt. Among 
the acids, tannic and acetic 
acid are perhaps the most 
usual and preferred by reason 
of their reaction upon the 
sulphate of lime, and the rela- 
tively mild action which they 
have upon iron if the acid 
should not find sufficient base 
in the feed-water and remain 
free. These acids are intro- 




FiG. 263. 



duced in the form of brewer's grains, molasses, oak-bark, etc., or in 
the form of a liquid or crystalline acid. The difficulty with this method 



CARE AND MANAGEMENT OF BOILERS 



289 



is the danger to the metal of the shell itself. In some few places 
where an acid water has been at hand it has been alternated or mixed 
with the basic water so as to oppose them to each other's action. 

The salts which are used are either the carbonate of soda, the chloride 
of barium, the tannate of soda, or the sodium triphosphate. The 
reactions of these with the sulphate of lime form a non-adhesive precipi- 
tate, and the soluble salt which results from the reaction with the lime 




Fig. 264. 



is removed by blowing down. The proportions of salt to be used with 
any water are to be determined on the basis of chemical analysis. To 
this class belong also the methods of which the use of zinc suspended in 




Fig. 265. 



the water is a type. While the scientific basis for the practice is not 
clear, its practical success in many cases for the purpose desired cannot 
be questioned. 



290 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

189. Previous Purification of Feed-water. The method which 
stands on the highest scientific plane with a boiler plant which must 
use a bad feed-water is to prevent the solid matter from getting inside 
the boiler at all. There are several methods for attaining this object. 

(1) The use of such forms of feed-water heaters as may properly be 
called lime-catchers (Figs. 265, 281, 282). The feed-water is heated 




in the heater to a point at which it precipitates all or most of its solid 
matter (paragraf 185). 

(2) The use of the methods of surface condensation which prevail in 
marine practice, whereby the same distilled water is used over and 
over again and no additional soHd matter is introduced with the feed- 



CARE AND MANAGEMENT OF BOILERS 



291 



water, except with so much of the latter as may have to go in to supply 
leakage and waste (Figs. 663, 664, and 665). The use of impure water 
to cool the surface condenser is entirely admissible. 

(3) A previous purification of the feed-water by chemical means. 
This means that the feed-water to be used in any day is introduced 
into a tank, and into such tank is 
thrown the necessary reagent to 
throw down the solid matter in 
the water. The milk of lime or 
hydrate of lime will transform the 
soluble bicarbonate into the insol- 
uble protocarbonate, and the chlo- 
ride of barium will form the sulphate 
of barium with the sulphate of lime. 
The precipitate thus formed can 
either be filtered out, or it can be 
allowed to settle and only the clear 
liquid is pumped into the boiler 
which contains the soluble sulphate 
constituents which remain after the 
reactions. The disadvantages of 
this method are obvious in the cost 
of the tankage, and the room which 
it will occupy, and the cost of the 
reagents used in the process. 

190. Filtration of Feed-water. The filtration of feed-water for the 
removal of either suspended solids or precipitates can be done in 
open filter-basins, or in close or pressure filters. The open filter-basin 
is the usual water-works method, whereby the water is made to pass 
through layers of gravel, sand, and charcoal in succession, and in each 
of which a certain proportion of the suspended material is caught and 
only the clear liquid passes through. The pressure filters operate on 
the same principle of forcing the feed-water through layers of successive 
fineness, but this will be done in a closed tank and under pressure 
instead of depending on the simple head due to gravity. Most of these 
filters operating under pressure are arranged to be reversible either by 
three valves, or a system of equivalent pipe-connections, so that the 
accumulated mud in the layers of the filter can be washed out by such 
reversed current. Otherwise provision must he made at intervals to 
remove the filtering material, cleanse it, aad replace it, during which the 
water either goes unfiltered or is filtered through a duplicate or reserve 
apparatus (Figs. 266, 267). Consult also paragraf 530 on oil-filtration. 




Fig. 267. 



292 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

191. Deterioration or Wear and Tear of Boilers. The conditions to 
which a boiler is exposed in service tend to wear it out. Many engineers 
have felt so strongly on this point that they have proposed to limit the 
life of a boiler in use, and to specify that a boiler is good for ten years, 
may be run at reduced pressure after fifteen years, but should be thrown 
out at the end of twenty. The causes which tend to wear out a boiler 
are partly inherent and unavoidable, and partly accidental so as to be 
avoided by care. The avoidable ones are usually acute forms of the 
sources of deterioration which are inherent and unavoidable. Deteriora- 
tion of boilers is caused by overheating, by unequal expansion and 
contraction and by corrosion. 

193. Overheating of Boilers. An injury to the heating-surface of a 
boiler from overheating is usually due to carelessness either in permitting 
the water-level to get so low as to expose the heating-surface uncooled, 
or to the presence of scale or grease. These have been already referred 
to in the previous paragrafs. The furnaces of internally-fired boilers 
and the tubes of sectional boilers are particularly liable to injury from 
overheating caused by grease. In sectional boilers, besides the oxida- 
tion due to overheating, a strain of great magnitude is set up in the 
straight-tube boilers, where the tubes tend to become of unequal length. 
In some forms of sectional boilers also, in which disengagement is 
inadequate and circulation impeded, a section may become overheated 
because the water cannot reach the metal. Sectional boilers whose 
units cannot be cleaned are especially open to the danger of overheating. 

193. Unequal Expansion and Contraction of Boilers. The intense 
action of the fire upon boilers tends to raise the temperature of the metal 
forming them, while an impact of cold air or cold water produces a 
tendency to cool and contract that metal. Where this action is local 
the boiler has a tendency to stretch out of shape, and strains are brought 
upon its structure which act to wrench and destroy the boiler, causing 
leakage and deterioration. These changes of shape may produce 
several consequences. 

(1) In fire-tube boilers they cause a leakage of the joints where the 
tubes are expanded into the heads. 

(2) The boiler has a tendency to change its shape, and therefore to 
alter the distribution or the proportion of strain which comes on its 
various lugs or supports (paragraf 133). In shell boilers this change 
of shape may produce such a super-position of strains as to cause a 
boiler to give way under them at a point where such combined strains 
may be concentrated. 

(3) If there are any defective welds in the plate of which the boiler 
is made, contraction of the layers of skin causes that lamination to 



CARE AND MANAGEMENT OF BOILERS 



293 





extend, and finally to develop a blister or bag (Fig. 26). In steel 
plate a blow-hole will be the occasion for similar action. 

(4) The contraction and expansion of a boiler with lapped joints 
prodvices an effect which has been called " grooving." The effort of 
the two contiguous plates to flex into line 
with each other when they are pulled length- 
wise (paragrafs 32 to 40) causes the protect- 
ing scale of oxide of iron to be broken off at 
the point of greatest flexure. Fresh rust 
forming there and again broken off by the 
flexure of the joint results ultimately in the 
erosion of the metal and the formation of a 
groove at this point, whereby the strength 
of the plate is gradually reduced. Figs. 268 
and 269 show a groove of this sort and its 
location. They are often deep enough to 
take the blade of a knife, and are to be 
detected in most cases by its use. They are 
also revealed frequently by the presence of a 
stain of oxide of iron upon the scale removed 
from the plate around the 
joint. Grooving is made 
worse when there are acids 
in the w^ater, and where 
the flexible part of the shell 

is joined to a stiffly-stayed or inflexible part, so that 
the bending action is concentrated. Such a place is 
the joint of the flange of the head of a boiler with the 
flat surface of the head. 

194. Corrosion External. The third source of deteri- 
oration of boilers is the corrosion to which they are 
exposed from the conditions of their use. This corro- 
sion takes place from the inside of a boiler and from the 
outside. 
External corrosion may be the result of any or all of the following 
conditions: 

(1) The action of the hot gases upon the heated plate which forms 
the heating-surface. If the fire is forced, or if the surface is covered 
with a thin scale which prevents rapid transfer of heat, the metal will 
be heated so that it will react with oxygen in the gases and become 
rusted or corroded. This difficulty is aggravated by the presence of 
moisture in the gases, either from the coal, as water present mechanically, 



Fig. 268. 



294 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

or from the combustion of hydrogen to water. This condition is favor- 
able to rapid action on the iron from carbonic acid, or sulfurous acid 
resulting from the oxidation of carbon, or sulphur in the fire-box. 

(2) From leakage. This may occur from seams, around rivets, where 
the tubes enter the tube-sheets, around the dome-joints, and at the 
joints of the hand-holes or manholes in shell boilers. In sectional 
boilers, in addition, will be the leakage caused around joints of the caps 
and that which is caused by unequal expansion of tubes in their headers. 
In internally-fired boilers, where the water-legs are closed by massive 
rings at doors and bottoms, leakage is apt to occur from differences of 
temperature due to defective circulation. The leakage from valves 
which are not thoroughly packed or tight upon their seats is also a 
further occasion for corrosion. This moisture not only corrodes of 
itself, but is the occasion for forming an active corrosive agent with 
carbonic or sulfurous acid; and if the water exerts any mechanical 
action upon the rust, scales tend to loosen and expose fresh surfaces to 
corrosive action. 

(3) The presence of lime in the setting of brick-set boilers is another 
occasion of external corrosion. The heat of the fire and its gases causes 
the lime to become calcined to the hydrate, and in this form it is likely 
to exert a corrosive influence where it touches the metal. 

External corrosion is to be detected by careful inspection, and the 
setting of the boiler should be such that this inspection should be 
possible. 

195. Corrosion Internal. The corrosion which takes place inside a 
boiler is more rapid and injurious than the external corrosion. It may 
be due to one or all of several causes. 

(1) The presence of acid in the water undergoing evaporation. The 
source of this acid in the water is often determined by local conditions. 
In the mining districts where sulfur prevails in the coal or in the 
surface-water and, worse than that, in the mine-water, the sulfurous 
acid which results is very actively corrosive upon iron. Nitric acid in 
the form of decomposable nitrates and nitrites is present in waters which 
have been contaminated with sewage or which contain organic matter. 
Water from bogs or peaty deposits containing vegetable matter in 
decomposition will contain the earthy or humous acids, formic, etc. 

(2) Perhaps the most trouble in boilers is caused by the corrosive 
action of the acids due to decomposition of the lubricants. The reaction 
on boiling animal oils, tallow, etc., breaks such material up into stearic 
and oleic acids, both of which are corrosive to iron. The oil comes into 
the boiler with the feed-water from condensing engines where pains 
are not taken to prevent it (paragrafs 246, 307, 528), and will undergo 



CARE AND MANAGEMENT OF BOILERS 295 

this trying-out process. The active element of corrosion in sea-water 
and water used in marine boilers is hydrochloric acid, which results 
when the chloride of magnesia present in sea-water is boiled. The 
heat decomposes the chloride into the hydrate of magnesia and hydro- 
chloric acid, which latter attacks the iron. 

(3) From galvanic action between the iron of the boiler and some 
metal which is electropositive to iron. Such metals are copper and 
brass, which form with iron a galvanic couple, and in waters containing 
even weak acids, like carbonic acid, the iron undergoes oxidation and 
corrosion. Such metals for galvanic action would be found in copper 
stay-bolts, tubes, ferrules, and even in brass mountings of fixtures for 
feed-connections. Sea-going boilers are particularly liable to this kind 
of corrosion by reason of the presence of the acids in sea-water, and it 
has been found a convenient thing to hang a piece of zinc in the water- 
space of such boilers in order that by its presence, which furnishes a 
lower electric potential, the zinc might be the element attacked rather 
than the boiler itself. 

(4) Distilled water containing carbonic acid seems itself to be -cor- 
rosive of iron, under the conditions which prevail within a boiler. 
Laboratory experiments have not always been conclusive on this point, 
except with respect to water containing no air but carrying carbonic 
acid. 

(5) The water seems to have an erosive action mechanically against 
surfaces upon which it is thrown violently by the currents of steam in 
which the water will be carried in drops. 

Spattering followed by drying of the spattered water seems also 
to wash off and loosen the scale of oxide of iron and produce the effect 
of corrosion. 

The corrosion due to water is to be expected below the water-line 
or where the mechanical action of water may make itself felt near 
the water-line in the steam-space or in the pipe-connections. 

Corrosion, however, is often met in the steam-space of the boiler and 
manifests itself with somewhat of capriciousness. It has been found 
that a boiler in the steam-space may be kept quite hot by the non- 
conducting covering over it, and sometimes causes the corrosion to 
manifest itself more rapidly by reason of the high temperature 
producing a considerable expansion, and at a rate different from that 
of the oxide of iron, so that the oxide is cracked off and fresh surfaces 
exposed. 

196. Pitting, Wasting, and Grooving. The corrosion of a boiler on 
its internal surfaces usually takes place in one of three forms. The 
wasting is a gradual thinning of the plate all over, due to a uniform 



296 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

acid action whereby the iron is dissolved. It is not always easy to 
detect this, except by close inspection of the joints, and the indications 
around the rivets which show what the original and unreduced thick- 
ness of the plate should have been. 

Pitting is a curious and capricious eating of the plate in spots. The 
reasons for local corrosion of this sort are not easy to find. It is doubt- 
less often due to lack of homogeneity in the plate, so that it has been 
more disposed to yield to corrosive influence where cinders or similar 
impurities are present. Mechanical erosion is apt to produce the 
effect of pitting. 

Grooving is the corrosion which has already been referred to in 
paragraf 193, where the changes of shape cause a mechanical breaking 
away of the oxide of iron formed, so that fresh surfaces are continually 
exposed. When corrosive tendencies are present in the water, grooving 
goes on so much the more rapidly. 

It is a matter of discussion as to the best preventive of corrosion in 
boilers which are to go out of use. Some advocate the plan of pre- 
venting access of air by filling the boiler full of water. Others dry 
out the boiler by putting a charcoal fire in a brazier within it which 
disposes of the oxygen also, and any remaining moisture is absorbed 
by hydrate or chloride of lime. Then the boiler is closed. This is the 
English naval practice. Others again fill the boiler full of water and 
inject some oil which rises to the top. The water is then withdrawn 
slowly from the bottom, leaving a film of oil laid on by capillary 
action over the entire previously wetted surface. 

Minute and painstaking inspection of the interior surfaces of a boiler 
is necessary if danger from corrosion is to be guarded against. 

197. Repairs. GeneraL The repairs to a boiler are of the same 
nature as the operations in its construction so far as leaky seams or 
tubes and joints are concerned. The leakage at a tube-joint can be 
prevented by expanding once or twice, but after that the metal becomes 
hard or brittle and further expanding cannot be done. Locomotive- 
tubes are particularly liable to trouble of this sort, and the custom 
has prevailed of cutting the tube off at its two ends and inserting a 
snort length at one end, which should bring fresh and unfatigued metal 
to make the joints at the tube-sheets without renewing the entire tube- 
body. The piecing out of the tube is done by making the two ends to 
be joined into a. male and female cone, and then welding the lap of the 
two surfaces over a mandrel. In sectional boilers the repairs are usually 
renewals of the tubes in detail, the regrinding of joints between the 
caps and headers, and the like. All boilers with manholes will require 
that the gasket shall be renewed periodically, and usually at each time 



CARE AND MANAGEMENT OF BOILERS 297 

that the manhole-Ud is removed for purposes of cleansing and inspection. 
On shell boilers, however, it may be necessary to apply a patch. 

198. Patches. The failure of a part of the metal in a shell boiler 
where the entire plate does not have to be renewed may be repaired by 
putting a patch on the defective part. Such patches are of two kinds, 
the hard patch and the soft patch. The patch will be put on a boiler 
by cutting away the metal which has deteriorated, leaving a hole where 
the defective metal has been and including enough to come to the solid 
and unaffected metal around the edge. A piece of boiler-plate is then 
shaped to the surface which it is to cover, and of a size to cover the hole 
and lap over its edge so as to be riveted to the shell in lap-joint. The 
necessary holes are then drilled and the patch is riveted on in place and 
calked. Such a patch is as good as can be made, but a patched boiler 
is never as good as the unpatched plate, and the presence of patches 
usually indicates either defective material or hard usage. 

The hard patch just described will be used wherever possible, but 
it can only be used where riveting can be done. If the patch must 
be made at a place where riveting is impossible, the patch will be 
secured in place with bolts, but they will not make the joint as tight as 
the rivets, and consequently a packing of some sort must be inserted 
between the two plates and also around the bolts. This packing is 
usually for the ordinary soft patch a cement of red lead mixed to a 
paste with oil, and held by being formed into a rope or gasket by working 
it into unwoven lamp-wick. A rope of this paste and wicking is laid 
around on the inside of the bolts in the lap of the patch, and is com- 
pressed to fill the joint and make it tight. Such a patch, however, 
is not as reliable as the hard patch, and is liable to blow out under heat 
and deterioration combined with pressure. 



CHAPTER XII. 

BOILER-INSPECTION AND TESTING. BOILER-EXPLOSIONS. 

200. Boiler-inspection. The steam-boiler being an engineering con- 
struction and exposed to known strains, it becomes necessary that the 
person responsible for it should be able to inform himself concerning its 
condition and ability to withstand these strains. This is to be done by 
means of inspection by the eye of experience and skill. It involves a 
knowledge both of accepted practice and of the causes which tend to 
wear out a boiler, and judgment in deciding how far they have acted 
either to render the boiler unsafe at its former pressure or unsafe to use 
under any conditions. A proper and full inspection, therefore, covers 
all the points which have been made the subject of discussion in 
Chapters III to XI hitherto, particularly with respect to corrosion 
in its various forms, the effects of overheating, and proper care and 
design with respect to bracing and staying, and also the use of satis- 
factory appliances for the management of the boiler and the relief of 
any excess of pressure. Further than this, the inspector should satisfy 
himself that the boiler is able to withstand its working pressure by 
exposing it to a pressure somewhat higher than that which it is expected 
to carry, and then observing whether under such pressure the boiler 
shows any signs of weakness, deformation, leakage, or similar failure. 
It is usual to expose the boiler to a pressure-test equal to one and one- 
half times its ordinary working pressure. This is entirely safe with 
normal conditions, since the boiler was probably designed with a work- 
ing pressure of one-sixth of its calculated bursting pressure (para- 
graf 26), so that if exposed to three halves of one-sixth of its bursting 
pressure, it is only tested to one-quarter of the ultimate pressure. There 
are three ways of making this pressure-test. 

301. The Steam Pressure-test. The steam pressure-test is to close 
the orifices of the boiler, increase the safety-valve weight, and build in 
a fire under the boiler to make it test itself to one and one-half times its 
working pressure. The advantage of this method is that it exposes 
the boiler to the conditions of service with respect to strains caused by 
heat as well as by pressure. The objection to it is evident; that if 
the boiler is to fail under its test, its failure, by reason of the presence of 

298 



H 



BOILER-INSPECTION AND BOILER-EXPLOSIONS 299 

a volume of hot water, will be the occasion of a disaster. It should only 
be practiced, if ever, where proper pubUc safeguards can be applied. 

203. The Hot-water Pressure-test. The second method is to fill the 
boiler completely full of water, and with all outlets closed start a fire in 
its furnace. The water will expand more rapidly than the iron forming 
the shell, so that the expansion of the water will bring a strain upon the 
shell from within which can be graduated to the required amount. 
When the pressure is reached the fire is withdrawn. Water expands 
2-I-4- of its volume in passing from 60° to 212 F., and the boiler, being 
full, is subjected to this expanding strain. This method has somewhat 
the advantage of having the boiler warm or hot, and in case of failure 
or rupture of the shell the water escapes without doing great harm, 
since but little energy is stored in it. The heat condition, however, 
is not favorable to the inspection of the shell for deformation and 
leakage, and consequently the third method is more usual. 

203. The Cold-water or Hydrostatic Test. The hydrostatic test as 
usually made is to fill the boiler completely full of water, and then by 
means of a pressure-pump, operated either by hand or by power, to 
raise the pressure of the water in the boiler to one and one-half times the 
working pressure. This is done in the cold; and while the boiler is 
subjected to this internal pressure it should be carefully examined for 
bulging of the heads or other deformations, and for leakage which can be 
attributed to this tendency to go out of shape under pressure. Leakage 
will be manifest by the rapid lowering of pressure, since the comparative 
incompressibility of water makes a sKght leakage release pressure very 
rapidly. By putting a test-gauge upon the connections of the pressure- 
pump the boiler-gauge can be tested for accuracy at the same operation 
(paragraf 172). The only objection which has been urged against the 
cold-water test is that it is a severe one and may injure the boiler by 
overstrain, and that the pressure due to the water brought by the action 
of a pump is a different and more exacting one than would be brought 
by the pressure of the steam. The rejoinder to this is that if a weakness 
is to be developed, it is immensely to be preferred that it should be 
developed while the test is on than in service, and the large mass of 
water in most boilers precludes any very great concentration of the 
pump-pressure. The steam-pressure is a fluid pressure, and the water 
is as flexible and mobile hot as cold. The laws of most cities compel 
a hydrostatic test to be made once a year at least of all boilers which 
are under municipal control. 

204. The Hammer Test. In addition to the hydrostatic test for the 
resistance of the boiler to pressure and the detailed examination within 
and without by the eye of an inspector, much information as to the 



300 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

quality of the boiler as a construction will be given by means of a careful 
and exhaustive examination with a light hammer. The blow upon a 
loose rivet or a stay which is not doing its work will reveal by the dif- 
ference in the resonance the difference in its condition, its looseness, or its 
overstrain. The hammer will also indicate and reveal defects in the 
metal of the shell, the presence of cracks and similar weakness which 
may lead to a failure. Where the plate has begun to laminate and the 
beginnings of a blister have occurred, the hammer-blow will show that 
the spot is no longer solid at the point struck. 

205. Boiler-explosions. General. The disaster which is most feared 
in connection with a steam-boiler as a reservoir of accumulated energy 
is that which is called an explosion. An explosion results from a very 
limited number of immediate causes, but a large number of secondary 
causes may be looked for as bringing about the primary cause. 

The primary cause is a failure or rupture of the enveloping shell of 
the boiler due to a pressure or strain greater than the metal could resist. 
This interruption of the equilibrium or the destruction of the reserve 
of metal strength may come about by two different ways. 

(1) The boiler may be too weak for the pressure, so that it ruptures 
at its working pressure. 

(2) The pressure may become too strong for the boiler to withstand, 
and it ruptures at some point above working pressure. 

206. Boiler Ruptures because too Weak. The boiler may fail because 
it cannot withhold the pressure within it by reason of one of four con- 
ditions : 

(1) The original pressure at which the boiler has ordinarily been 
worked may have been fixed too high for a structure of that material, 
design, thickness, and construction. Such a boiler never was safe from 
the very first day it was used, 

(2) The boiler, originally strong and able to withstand the working 
pressure, may have become weakened by age, wear and tear, corrosion, 
or abuse. 

(3) The boiler, exposed to normal working strain, may have super- 
posed upon such strain an extra strain of contraction, local and sudden. 
This may come by low water and sudden introduction of fresh cold 
water on overheated plates, or cold air acting similarly. This is the 
rupture of which low water is apt to be the occasion. 

(4) A defect of workmanship or material which escaped inspection 
when the boiler was new may develop in service, and particularly under 
abuse. The boiler may not be as strong as it was supposed to be, and 
fails. 

It is obvious that the more familiar the inspector is with the con- 



BOILER-INSPECTION AND BOILER-EXPLOSIONS 301 

struction and sources of deterioration of boilers, the more reliable is his 
judgment with respect to fixing the working pressure upon an old boiler. 
It will be seen presently that if the rupture of the shell is caused by- 
working pressure, the disaster called an explosion will or will not follow 
according to the combination of conditions under which that rupture 
takes place. 

207. Boiler Ruptures from Excess of Pressure. The boiler being 
strong, perhaps new, may have the pressure within it raised to such a 
point that it is unable to withstand it, and fails at its weakest point. 
This is the condition in explosions above the working pressure or at 
pressures approaching the computed bursting pressure. This group of 
conditions has been the favorite field for erroneous theories with respect 
to the disaster called a boiler-explosion. Most of them have been based 
on the idea that an explosion of some sort takes place within the shell, 
creating a pressure suddenly within that envelope, which it could no 
more withstand than if a powder-explosion were to bring suddenly an 
enormous pressure upon such a flexible envelope. Those who have 
upheld this idea have explained the explosion from the union of oxygen 
and hydrogen, w^hich are the gases of the water, supposing them to have 
been dissociated by an overheated plate occurring with the condition of 
low water. A second theory of this sort has been that by reason of low 
water and overheated plate a sudden rise of pressure results from the 
coming in of the feed-water, causing an explosive sort of pressure 
within the shell which it could not withstand. A third and similar 
theory is that the water in the boiler gets into the condition called 
the spheroidal state, in which the bubbles of water are kept away 
from the red-hot plate by a film of steam, and which bubbles form 
steam with a concussive rapidity when that film of steam is forced 
out. This condition is met in forging or rolhng where water is used 
on red-hot metal and then struck with a hammer. 

It is difficult to realize the above conditions in a boiler, and when an 
explanation without recourse to them is to be found from accepted 
principles it does not seem necessary to search for less obvious causes. 

Furthermore, it can be proved (paragrafs 213 and 214) that in a 
boiler containing a relatively small weight of water, and particularly 
with ample heating-surface, the time required to pass from a low pres- 
sure to a higher one, which may be called the dangerous pressure, 
becomes surprisingly short, so that in the absence of an efficient 
safety-valve, or where it is inoperative, the steam pressure to rupture 
the boiler may be reached very soon after the outlets from it have been 
closed, unless proper precautions be taken with respect to checking 
the fire. 



302 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



208. Theory of Boiler-explosions. When it is remembered that the 
specific heat of water is unity, so that a large quantity of heat is absorbed 
in raising its temperature one degree, it will be apparent that when a 
large mass of water under high pressure lies within a boiler an immense 
reservoir of available energy is at hand. 

The boihng-point of water increases with the pressure, so that if the 
pressure on the surface of the water in a boiler is suddenly released and 
drops to atmospheric pressure, or nearly to it, a large quantity of water 
will form steam-gas upon the release of such pressure without the addi- 
tion of heat. When, therefore, a boiler ruptures under pressure and full 
of water, permitting the escape of steam instantly or with great rapidity, 
the tendency of the stored heat in the water is to cause it to form steam 
under the reduced pressure with equal rapidity. The formation of 
steam-gas from water is easily comparable under these conditions to the 
formation of carbon, sulfur, and nitrogen gases in the combustion of 
gunpowder. Hence the rupture of the shell causing a release of pressure 
on the water brings about a condition analogous to the touching of a 
flame to a gasifying substance like powder, and the water flashing into 
steam-gas is the thing which explodes. If this operation is retarded, 
the energy is gradually released in forcing the water out 
through a small hole, and no disaster follows the rupture. 
This is the element of safety of the so-called sectional 
boilers. 

209. Energy Resident in Hot Water under Pressure. 
It can be shown by a simple diagram that an enor- 
mous quantity of energy is stored in a cubic foot of 
water at high pressure. If the base of the cylinder in 
Fig. 270 be supposed to have one square foot of area, 
and at its bottom a cubic foot of water is inclosed below 
the piston, so that upon the application of heat to that 
water the piston would have a tendency to rise under 
one atmosphere of pressure on it, the water would form 
steam to fill 1700 cubic feet. If, however, the pressure 
be increased upon the piston, the specific volume of 
steam at such higher pressure diminishes, while the 
amount of heat necessary to make the water into steam 
increases. The cubic foot of water at seven atmos- 
pheres or 103 pounds, instead of occupying 1700 cubic 
feet, would occupy but 274, because the piston would 
be held down by a pressure of 14,832 pounds. If it be conceived 
that. similar water in the bottom of that cylinder was not quite hot 



w 



J=3 



Fig. 270. 



BOILER-INSPECTION AND BOILER-EXPLOSIONS 303 

enough to make steam at that pressure, but was hot enough to 
make steam at a somewhat lower one, it will be apparent that the 
water when the pressure was released would be able to lift such 
weighted piston through a good many feet. A simple calculation 
shows that if this energy be represented in foot-pounds, it is able to 
carry the weight represented by a boiler-shell, or a part of it, through a 
good many hundred feet, and to produce the effects which have been 
observed to attach to the most disastrous explosion. 

210. Reaction in Boiler-explosions. It happens not infrequently that 
when the rupture of the shell from excess of pressure or weakness has 
permitted a partial escape of pressure, the water in the shell seems to be 
lifted by the sudden release of pressure on that side of the boiler, and the 
unbalanced pressure produces a reaction; or the water itself falls back 
against the part opposite the rupture, producing a strain which the 
alread}^ weakened shell cannot withstand, and thereby makes so large 
an opening for the release of pressure that the formation of steam-gas 
is almost instantaneous, and the boiler is driven out of its setting as a 
rocket is driven by the reaction of gas behind it. As a rule the Hght 
portions of a boiler after rupture are found in the direction of the initial 
rent, while the more massive pieces are driven by the reaction of 
unbalanced pressure in the opposite direction. This reaction-phenome- 
non resembles concussive ebullition (paragraf 236) in that a stress 
almost like that from a solid blow is brought by it against that part 
of the boiler which remains in place. 

211. Procedure when a Boiler is in Danger of Rupture. It would be 
manifestly unwise to release the pressure suddenly from a boiler which 
was already under a great strain and in danger of rupture. To do so 
would be to invite the reaction caused by the lifting of the water, and 
the possible superposition of strains from this cause. The opening of a 
large throttle-valve or of the safety-valve may act in the same way, 
and it is doubtless this combination of strains which explains the fre- 
quent failure of boilers when the day's work is just beginning and steam 
is turned from a boiler into a cold pipe, where it condenses and makes a 
reduced pressure, so that the steam rushes from the boiler at higher 
velocity than usual. A large valve should be opened with exceeding 
caution, slowness, and care under these conditions. 

The proper procedure is to withdraw the fire and permit the boiler to 
cool off gradually, and so permit the dissipation of pressure by these 
means. The fire can be checked by dumping it or by throwing ashes or 
dirt upon it. If great confidence is felt in the ability and strength of the 
boiler, the blow-off valve can be cautiously opened for the relief of 



304 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

pressure slowly through that opening. The heat stored in the water 
is thus disposed of, and after the boiler is empty of water it is com- 
paratively safe. The escape of pressure through the blow-off valve is 
also unlikely to cause difficulties from reaction. 

213. Heating Effect of Steel Plate and Cooling Effect of Water. If 10 

square feet of plate one-quarter of an inch thick be overheated so as to be at 1000° 
F., it will represent 100 lbs. weight of iron, with a specific heat of 0.112. If water 
come on that plate at a temperature of even 300° F., it will cool the plate by a 
transfer of heat to the water; whence 

Q =w Xc' X {t,- t) = 100 X 0.112 X 700 = 7900 

units of heat received by the unknown weight of water. It takes about 1000 units 
of heat to vaporize a pound of water under the pressure corresponding to 300° F., 
or that plate would vaporize about 7.9 lbs. of water only, or less than a gallon, in 
being cooled to the temperature of the rest of the boiler. The volume of one pound 
of steam at 300° is 6.28 cubic feet, so that this steam would occupy but 7.9 X 6.28 
or 49.6 cubic feet in the boiler. 

213. Time required by Boiler to absorb Heat and Pressure Energy. The 
following formula, due to Zeuner, shows the time to be allowed to a boiler to pass 
from one pressure or temperature to another. The lower pressure (t) may be that 
of the cold feed-water, in which T will give the time required to get up the steam- 
pressure corresponding to any higher temperature (ty); or t may correspond to the 
working pressure, and t-^ be the temperature corresponding to a pressure which will 
endanger the shell. 

Let T = time in minutes elapsing between the period when a lower temperature 
(0 prevails and that at which (t^) will be the temperature when all 
outlets are closed for steam or discharge of heat ; 
t = temperature corresponding to the lower pressure; 
ti = temperature corresponding to the higher pressure; 
W = weight of water in the boiler; 

Q = quantity of heat in B.T.U. transferred to the water in the boiler per 
minute. 

Then ^=^^- 

The quantity Q for any boiler is found from the expression 

/ heating-sur- \ / pounds of water \ / the quantity of \ 

/ face of boil- | / evaporated per | | heat absorbed | 

I er in square I liour per sq. foot I I in evaporating | 

V feet / \ of heating-surface / ^ 1 lb. of water / 

«= ^0 

The third factor in the numerator is 966 at atmospheric pressure. For higher 
pressures it may be called 1000, to make round figures. 



BOILER-INSPECTION AND BOILER-EXPLOSIONS 305 

Illustrations of the application of this formula would be: 
Case 1. Locomotive Boiler. 

W = 5000 lbs. of water; 

Grate-surface = 11 sq. ft., and each square foot burning 60 lbs. of coal will evaporate 
7 lbs. of water per pound of coal per hour, or 77 lbs. of water per 
minute ; 
t = working pressure of 90 lbs. = 319° F.; 
t^ = dangerous pressure of 175 lbs. = 371° F. 

t^- t = 50°+ F. 

„ ^ 5000 X 50 „ ^ . , 

Hence ^^ 77 x 1000 ^ ^'^ "^'"^^"^- 

Case 2 Marine Boiler, Flat Surfaces. 
W = 79,000 lbs. of water; 
Heating-surface = 5000 square feet, evaporating 3 lbs. of water per hour, or 250 lbs. 
per minute; 
t = working pressure of 37 lbs. = 262° F. ; 
tj^ = dangerous pressure of 60 lbs. = 291° F. 

t, - t = 29° F. 
„ 79000 X 29 QT . , 
^ = 250 + 1000 ^^•^"^^"^^^^^- 

Case 3. Fire-engine (a) Boiler to get up Steam. 

W = 93 lbs. of water, or about 1^ cu. ft.; 
Heating-surface = 157 sq. ft., evaporating 1 lb. of water per hour, or 2.6 per minute; 
t = atmospheric pressure, or 212° F. 
^^ = workmg pressure of 329° or 100 lbs. pressure; 

t, - t = 117° 
Then T= ^1-^^ = 4.2 minutes. 

Case 4. Same Boiler (6) to become Dangerous. 
W = 338 lbs. of water; 
t, = 200 lbs. pressure, or 388° F. 
Then t^ - t^ = 49°, 

A T 338 X 49 ... ^ 

and ^^ 2.6X 1000 ^ ^'^ "^^""^^^- 

It will be apparent that the danger increases with the heating-surface, and 
diminishes with the greater weight of water contained in the boiler. 

214. Steam Boilers as Magazines of Explosive Energy. Nystram, p. 393, 
gives dynamic work of gunpowder at 150,000 to 200,000 foot-pounds per pound of 
powder. Even at atmospheric pressure, the energy resident in one cubic foot of water 
heated to form steam-gas at that pressure is 

1700 X 144 X 14.7 = 3,598,560 foot-pounds, 

which if all released at once as gunpowder gasifies would bear a ratio of destructive 

energy of oqqqqq ' ^^ nearly 18 times that of such powder. 



PART III. 
CHAPTER XTII. 

BOILER PLANT AUXILIARIES. 

220. Introductory. In the development of the previous chapters 
the logical basis has been the simple problem outlined in Fig. 1 where 
from the pile of coal and the water tank two streams of potential energy 
have been directed into the boiler and there transformed into a mechan- 
ical available force. These elements are present in the simplest power 
plant: they are never absent from the largest and most complicated. 
The effort has been heretofore to keep to the universal principles, which 
are not affected by the size of the plant whether large or small; and 
where alternative methods have been presented, these were coordinate 
in importance, no matter on what plane the plant is to work. 

When the plant becomes a large one, burning a large weight of fuel 
per day or per- hour, and where the problem of the number of, men and 
their cost becomes financially significant, it may be worth while to plan 
and to expend in first cost for a group of auxiliaries in the way of steam 
machinery whose purpose will be either a diminution of the demand 
for human labor by replacing it by mechanical appliances, or an increase 
in economy and efficiency in the use of fuel, or both of these. Such 
machinery is called boiler plant auxiliary machinery or boiler plant 
auxiliaries. In the diagrams of Figs. 2 and 3 such auxiUaries are 
presented either as driven from the main engine by transmitted power, 
either electrically or through shafts and belts, or as independent aux- 
iliaries, each having its own steam cylinder receiving steam from the 
common main boiler plant, or from a donkey-boiler if the former is not 
in operation. If the plant is small or temporary, it may not be worth 
while to provide these auxiliaries : if large or permanent it usually pays 
to do so. 

Such auxiliaries belonging in the boiler plant will be: 

1. Mechanical coal -handling plant . 

2. Mechanical ash-handhng plant. 

3. Mechanical stokers. 

4. Heaters for feed-water. 

5. Special auxiliaries for a particular plant. 

306 



BOILER PLANT AUXILIARIES 307 

The term auxiliaries must also be applied as used in Fig. 3 to the 
essential apparatus required for the boiler plant as: 

6. Boiler feeding, 
7<. Artificial draft, 
and for the engine-room auxiliaries proper such as: 

8. Condensers. 

9. Circulating and air pumps. 

10. Lubricating oil pumps. Special pumps. 

11. Special engine-room machinery. 

The middle series, 6 and 7, being essential to any plant or as alternates 
for an essential, have been already referred to; the last four will have 
a chapter of their own in later treatment. The present chapter is to 
enlarge upon the first five. 

231. Coal-handling Machinery. The labor of handling the fuel for 
a locomotive developing about 1000 horse-power is so severe that one 
man cannot stand the strain for more than three or four hours without 
a period of rest. When this same power is distributed in several fire- 
boxes and with fixed grates, and where the fireman must also look after 
the ashes and work for a ten-hour shift, the Hmit is from 250 to 300 
horse-power, depending on the fuel and its quality. 

If the fuel has also to be handled by human labor from bins or pockets 
to the boiler front, additional labor is called for; and if the coal must 
be carted from yards or boats or cars and delivered to the local bin an 
added charge in its price is incurred. 

Large metropolitan and other plants therefore in recent years have 
been seeking the water front of navigable waters, and have been group- 
ing themselves along the railway lines where there is no water, Avith 
spurs from the main line into the yard of the plant. The purpose of 
this is to handle their fuel in car or in boat-load lots. The principle of 
adequate storage has also been considered, so that in case of ice in the 
river or snow on the rail, or where for any other cause (such as a labor 
dispute) the regular weekly or daily delivery of coal was interrupted^ 
there should be a reserve on hand to prevent a shut-down for lack of fuel. 

From the boat at the wharf or bulkhead, the coal must be lifted in 
skips loaded by hand in the hull and then run on rails to where they 
will be dumped or emptied. Or, elevators of the type used for grain 
may be lowered into the hull and there charged, and the coal passed on 
to conveyors. For the boat and wharf combination, the coal may be 
piled upon the wharf or adjacent land, or put in elevated pockets. 
If piled, it must be handled again by elevators and conveyors. If the 



308 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

pockets are outside the building of the boiler plant, they can deliver into 
cars on grade and the latter be run in to the boiler-fronts on indus- 
trial indoor railways. 

Probably the best way of all is to deliver by elevator or conveyor or 
combinations into elevated bins or pockets within the building of the 
boiler plant on levels above the firing-floor. In cities this can be done 
by dumping by gravity from the street carts into steel cars below the 
street level: these cars are run on tracks to a vertical elevator within 
the building or outside of it, and raised to the top of the pockets. They 
are then run over the pockets and dumped. These pockets have a 
sloping or hopper bottom (see Fig. 695) vv^hose angle is greater than that 
of the angle of friction of coal, and these hoppers converge to a descend- 
ing pipe — say of 12 inches diameter — through which the coal is led to 
the desired boiler-front. The foot of the pipe may be closed with a 
valve, parting like the two halves of a clam-shell digger, or the bottom 
may be left open, coming down so near the floor that the cone of fuel 
shall not have an inconvenient base with the pipe orifice as its apex. 
When the cone is in place and untouched by the shovel or stoker no 
more coal can flow down. 

The modifications of this plan by special conditions are numerous. 
For example, with car-load delivery from a hopper-bottomed coal car 
on an elevated trestle, the pocket will be below the track, and usually 
outside the building. A conveyor will bring the coal to an elevator 
within the building, and deliver in turn to a second conveyor, which 
fills small pockets over each boiler or stoker. The type of elevator and 
conveyor must be chosen with regard to the special service required. 
With the masses of the coal lumps, the bucket-types on chains are usu- 
ally better adapted than the faster-moving belt-conveyors. Such bucket- 
chain types combine both elevating and transporting functions in one 
system. Instead of conveyors, industrial coal cars can be used on indoor 
railways; or the pockets may be indoors and elevated over the fire-room 
floor, etc. In recent large metropolitan installations where ground is 
costly and the batteries of boilers have been put over each other in 
successive stories, the plan of an overhead storage in pockets of perhaps 
10,000 tons capacity seems to be by far the best (Figs. 695 and 696). 

223. Ash-handling Machinery. A coal which has only ten per cent 
of ash and soUd matter to be rejected from the bottom of the grates will 
be considered above the average. This means that 200 pounds of 
refuse must be disposed of for every ton burned. 

This should also be handled mechanically and gravity utihzed as far 
as possible. It means a transverse tunnel or duct running on a level 
below the firing-floor under the ash-pits of all boilers, and with metal 



BOILER PLANT AUXILIARIES 309 

hoppers forming the bottoms of such ash-pits. From these hoppers 
after cooHng and quenching the ashes may fall on opening the hopper 
bottom either into cars or upon a conveyor which shall carry them to 
a central point from which they shall be elevated and discharged into 
carts or cars for removal. In many cities such removal must be con- 
tracted for^ as the quantity exceeds the normal capacity of municipal 
service. 

At sea, the ash is elevated and thrown overboard by what are called 
ash-ejectors, utilizing either atmospheric pressure ^or a flow of sea-water 
from a steam jet to lift and discharge. 

In shore plants the use of forced draft in the ash-pit compels that 
the hopper and its closure be practically air-tight, and no water can be 
used in the ash-pit. The tunnel or duct under the floor-level is also an 
expensive adjunct, but it is practically always justifiable in a large 
plant. 

233. Mechanical Stokers. The same arguments advanced in para- 
graf 221 for handling the coal from without into the plant upon the 
firing-floor apply also to the firing itself or the delivery of the fuel into 
the fire-box. There are also some additional points apphcable. By 
mechanically supplying the fuel to the fire the supply of heat units is 
constant and uniform, and hence a complete and smokeless combustion 
is much more probable. Men prefer to fire hard and then to rest after 
it, rather than to fire easily and continuously without stopping to rest. 
Particularly in bituminous coal firing and with rapid combustion, the 
mechanically fed fire secures the initial coking and subsequent incan- 
descent periods with more certainty and regularity than hand firing is 
likely to do, with the type of man who keeps to firing as an art and 
vocation. 

With mechanical stoking, the fire as a whole is at all times in the 
same condition. In certain cases, where a peak or maximum in the load 
curve appears, the regular' supply of heat units may need to be exceeded 
for a time, but this can be met by special hand service, or particularly 
by the use of forced draft, increasing the rate of combustion for the 
time. 

The fuel is led down from the pocket or bin overhead through a tube 
to a flat or wedge-shaped hopper in front of where the firing-door used 
to be. The dehvery on to the grate from this feeding hopper may be 
through a space which is open to the grate on one side, where the angle 
of friction of the coal lets just so much coal pass per minute under a 
regulating plate. Or a cylinder with radial vanes or wings turning 
within another hollow cy Under at a determined rate may measure off 
from the hopper the quantity which fills one of these segments. The 



310 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

traveling-grate principle may be used (Figs. 175, 271) or the alternately 
reciprocating bar (Fig. 272) or the step with tipping effect (Fig. 273) or 
the underfed principle of Fig. 274. The latter possesses considerable 
interest for special grades of coal, inasmuch as the distillation takes 




i 



place from the bottom upward, and the gas without admixture of air 
passes up through the burning mass above it, becoming heated and 
ready to ignite when it escapes from the top. The coal flows laterally 
downward to the sides and com.bustion is complete when the coal 



BOILER PLANT AUXILIARIES 



311 



reaches the Hmit of motion, as in all the designs. If now the motor 
driving any of the stokers be controlled by a valve operated by a dia- 
fram or piston upon which the steam pressure is balanced by a weight 
or spring, the variations in pressure can directly and automatically be 
made to vary the speed of the grate-motion. This system for a con- 
stant load or one which varies within narrow limits has the advantage 
of replacing hard and exhausting human labor by substituting for it 



^If^y^P^^^^ 




AMtaiCAN BANK NOTE M..N,r, 



Fig. 272. 



intelligent control of inanimate force. A form is also in use where the 
inclined or step bar is operated and the fuel fed down the bar from 
each side toward the center, where it escapes as ash at the bottom. 

Mechanical stoking has not done its best work with the hard varieties 
of anthracite coal with which the fireman's labor is the least. Fig. 274 
is at its best in comparison with the others with those bituminous coals 
which are fat and which melt and cake with the heat. 



312 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




BOILER PLANT AUXILIARIES 



313 




314 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

The objections to the travehng type of grate in stokers has been that 
only a part of the nominal grate area is covered with heat-giving fire. 
The front inches are covered with black coal, and if the travel is slowed 




Usual 
Ash Door 



Fig. 275. 



down to favor the front ignition, the back end is not effective unless the 
fireman in charge is specially attentive. The grate also gets no pro- 
tection from any ash on its surface, and burns out sooner than the 
stationary grate with hand-firing. A type of mechanical shovel stoker 
is in use on locomotives and a form for stationary use with overhead 



BOILER PLANT AUXILIARIES 315 

pocket and feeding-tube is shown in Fig. 275. The coal is mechanically 
forced forward by the ram A into the hollow cylinder D and from the 
latter projected forcibly by the spring action of E through the swing of 
C when the spring is released. The impeller C has a graduated sweep, 
and 'throws the coal a short distance when the swing is Hmited, but all 
the way to the back of the grate when the swing is ample. Grates 
eight or more feet deep can be covered. The fireman cleans and slices 
through the ordinary door, so that some of the advantages of closed 
front stokers are sacrificed in order to work with the less costly grate. 

224. The Forced or Induced Draft by Fan and Motor or Engine. In 
this same group of boiler plant auxiliaries is the engine or motor for 
driving the fan or blower which furnishes air to the fuel in the furnaces 
as discussed in paragraphs 127-129. In electric power plants these 
fans will be motor driven; in others they will have their own engines. 

225. Preheating the Feed- water. Since the fire is the source of 
all heat energy (paragraf 105) the heat to raise the feed-water from 
its temperature in the suction-tank to that at which the water boils 
at that pressure must be supplied, as well as that necessary to make 
the water into steam. If the total heat of each pound of steam be 
called T and the temperature of the unheated feed-water be called 
t, the total units of heat furnished to that pound may be called 
T — t = X. If, now, by means of heat which would otherwise be 
wasted and lost this feed-water be preheated before entry into the 
boiler to a temperature f, then the heat to be suppHed from the fire 
will be the quantity T — f, which may be called y. Then the quantity 
X — y = f — t will be the saving of heat per pound of water due to 
such preheating. Then for any time in which a quantity or weight 
of water W is fed to the water, the percentage of saving from such 
preheating will be 

W {x - y) 100 (f - t) 



Wx L + r-t 

where L is the heat of vaporization of water at the pressure corre- 
sponding to the boiling temperature T^ attaching to that pressure. 

This waste heat utilizable for preheating the feed-water is to be 
gotten either from the products of combustion in the flues on their 
way to the chimney, or from the heat rejected in the exhaust steam 
from the engine cylinder. Flue heaters are usually called economizers. 
When the engine operates condensing (paragraf 500) the pressure in 
an exhaust steam-heater will be less than atmosphere, and special con- 
ditions must be regarded, to be referred to in paragrafs 227 and 306. 



316 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

33^. Flue Heaters or Economizers. Flue heaters are of special 

value with water-tubular or sectional boilers of short period of contact 
between tubes and gases; or when for any reasons the flue temperature 
is high because of a high rate of combustion. Fig. 276 shows the usual 
plan of arranging the economizers with a by-pass flue to the chimney: 
Fig. 278 the general lay-out, and Fig. 277 the end elevation. The 
ordinary proportion of pipe is to give 4i to 5 square feet of heating 
surface for each boiler horse-power, using 4-inch tubes about 9 feet 




By-pass Flue 



v//////////////////////^^^^^^^ 



^ ; ■ ^ 



^ 



Economizer 



Economizer 




Fig. 276. 



long. The scraper outfit is necessary to keep soot and tarry matter 
from making a non-conducting cake on the tubes by condensation. 

The advantages of the flue-heaters are that they heat the water to a 
high temperature, and higher than the exhaust-steam heaters when 
other things are equal. The exhaust-steam is apt to be at a tem- 
perature not much above boiling-point, whereas the flue gases may 
easily be hotter than 500° F. 

The objections to them are: 

(1) That the difficulties from unequal expansion are very great, 
and unless special care is taken both in manufacture and design these 
will cause leakage. 

(2) They are exposed to corrosion on the outside by the gases from 
most of the fuels, and particularly when a Ught covering of soot has 
coated the outside of the coil with an absorbent covering which holds 
moisture and acids in contact with the metal. 



BOILER PLANT AUXILIARIES 



317 



(3) When feed-water is not circulating through the coils so as to 
keep them full of water, they will make steam which will escape through 
the check-valve into the boiler, leaving a part of the heater exposed 
to overheating. 

(4) They require to be cleansed from soot or tarry deposit by 
careful scraping in order to be 

kept efficient. The formation of 
scale within the pipes will take 
place with waters having solid 
matter in them. Figs. 277-8 
show the usual form of econo- 
mizer with provision for external 
scraping, which becomes partic- 
ularly easy with the vertical 
type. 

It is safe and convenient either 
to put a relief or safety valve in 
connection with an economizer, 
or else to see that no stop valve 
intervenes between it and the 
relief valve on the boiler. The 
economizer is in fact a boiler, 
and if the pump valves are tight, 
the only escape of pressure of 
steam formed in the heater dur- 
ing a stop must be forward 
through the boiler check. If this 
outlet is closed the pressure may 
accumulate dangerously. 

Feed-heaters are always placed between the pump and the boiler, 
to give solid water for the pump and to keep its water cool as possible. 

221, Exhaust Steam Feed-water Heaters. In a steam-engine which 
discharges its exhaust steam at the pressure of the atmosphere or above 
it, there remains in that steam at least the amount of heat which made 
water at 212° F. into steam at atmospheric pressure. This is 966 units 
of heat per pound. If this heat could be abstracted by bringing the 
steam into contact with the feed-water, the heat otherwise wasted 
would be economized, and this is the basis and the limit of heaters of 
this class. For if the feed- water be put at 50° F. as an average tem- 
perature for the year, and it be assumed that in an efficient heater the 
temperature of the feed could be raised to 200° F., or through a range 
of 150°, then the entire weight of exhaust steam from the engine W with 




Fig. 277. 



318 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




BOILER PLANT AUXILIARIES 319 

a heat-carrying capacity of 966 units per pound could heat a weight of 
feed-water w through the 150° range, since the equahty must prevail that 
W X 966 = w X 150 less losses by radiation and in transfer. If the 
relation between 150 and 966 be called one-sixth to allow for some loss, 
then the weight of water undergoing heating in the heater should not 
exceed six times the weight of steam passing through the heater in the 
same time, else the heater will not heat it so hot as above computed. 
Stated otherwise, if the weight of steam be called the same as the weight 
of water which is to replace it in the boiler, then the heater can only 
utilize one-sixth of the heat of the steam exhausted, and the rest must 
be saved otherwise if at all. If the engine is to operate condensing, 
with an exhaust pressure below atmosphere and a temperature below 
212°, there will be fewer units of heat to be imparted to the feed-water 
than in the foregoing computation. If, however, the auxiliaries are 
operated, as is often the case, with an exhaust to atmosphere while the 
main engine is condensing, it may be worth while to arrange two feed 
heaters in tandem for the feed-water. The first one is in the main 
engine exhaust circuit, heating the feed- water part way; the second 
receives the feed-water from the first and is heated by exhaust from 
the auxiliaries. Should it happen, however, that the weight of the 
atmospheric exhaust from the auxiliaries exceeds the above one-sixth 
of the total feed-water used in the plant, then the first or main engine 
heater would be an unnecessary complication and expense, since the 
auxiliary exhaust would handle all the feed-water which the plant 
required, and effort should be directed to improve the vacuum and 
lower the temperature of the main engine exhaust. The condens- 
ing engine exhaust will give from 110° to 120° as the feed-water 
temperature. 

Feed-water heaters are usually designed without specific reference to 
any one set of conditions of feed-inlet or exhaust steam temperature. 
Hence an average proportion gives one square foot of heating surface 
in closed-circuit heaters for each 90 pounds of water per hour passed 
through the heater when the steam is above atmospheric pressure. If 
the water rate be called 30 pounds per hour (paragrafs 8 and 10), 
this is one-third of a square foot per horse-power. The ratio of one to 
thirty-five or thirty-six (paragraf 9) which this bears to the heating 
surface in the boiler results from the fact that the heating range is much 
lower in the heater than in the boiler, and the ease and speed with which 
steam parts with its latent heat as compared to its reluctance and slow- 
ness to absorb that same heat. In condensing engine heaters, the heat- 
ing surface should be increased to one and one-half square feet for the 
same weight of water. As the heating and absorbing masses draw near 



320 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

to each other in temperature the rate of transfer of heat to the cooler 
body grows less. 

There are two great classes of exhaust-steam heaters. The first are 
known as open heaters, in which the feed-water comes in direct con- 
tact with the exhaust-steam and withdraws its heat by direct conden- 
sation. The other class are called closed heaters, in which the steam 
and water are in separate circuits of pipes or coils which have the 
steam on the outside and the water within, or the reverse. The open 
heaters are in some respects the more efficient, since the steam and 
water come together, and since sufficient heat is often imparted to 
the water to bring it to that point at which it will precipitate the 

' IU|alati]ig Valve 

Cold Water Inlet 




Fig. 279. 



solid matter which it contains. This class of heaters have been called 
lime-catchers. Fig. 265 shows a form of this class of heater in which 
the water passes over the set of trays within the heater which are 
surrounded by the exhaust-steam. The hot water deposits its solid 
matter most rapidly in the thin films in which it escapes over the 
bottoms of the trays, making removal of such material complete, and 
the cleansing of the trays easy and rapid. Figs. 279 and 280 show 
other forms. Figs. 281 to 284 show types of the tube or coil-heaters of 
the closed class. The tubes are apt to be of copper or brass, in order to 
be rapid conductors, and are curved so as to yield easily to the con- 
dition of rapid expansion and contraction to which they are exposed. 
It is convenient to pass the steam through the inside of small coils, 
because the only deposit in the small tubes is the lubricant, which is not 



BOILER PLANT AUXILIARIES 



321 



so difficult to remove. The arched or flexible forms given to the tube- 
plates and corrugation of the tubes also provide for these inequalities 
of expansion. 

Such steam-heaters will act partly as surface condensers if they have 
an abundance of surface, but 
care should be taken that the 
resistance offered to the ex- 
haust should not impose a 
back pressure upon the engine- 
piston, which should cost more 
coal to overcome than the 
saving of fuel caused by the 
heater. This is a matter of 
simple calculation when the 
back pressure is observed with 
the heater in action and out of 
action. Feed-heaters for con- 
densing engines with the steam 
circuit below atmospheric 
pressure must necessarily be 
closed heaters. 

228. Superheating of Steam. 
The historic researches of Reg- 
nault which are embodied in 
all steam tables (paragrafs 23 
and Appendix 566), have 
proved that for every pressure 
of steam there is a corre- 
sponding temperature and 
boiling point. This equilib- 
rium between pressure and 
temperature is therefore a 

precarious one in any mass of steam and liable by change in either 
to be disturbed from that previously existing. If a pound weight of 
steam be enclosed in a vessel of the proper volume, and this volume 
is full of dry invisible steam gas — that is, if this volume be saturated 
with steam at that pressure, so that it will hold no more — the equi- 
librium of temperature and pressure can be upset in four ways: 

1. The pressure can be mechanically increased from without. There 
is not temperature enough to meet this higher pressure, and some of the 
weight of steam must go back to water in the form of a mist or vapor — 
even drops: 




Fig. 280. 



322 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



2. The temperature can be lowered. At once there is not heat 
enough to keep all that weight of steam as gas, and some of it goes back 
to water, or condenses, as in case 1. 

3. The preiLJLure can be lowered without coohng. The temperature 
is now too high for the pressure. If there was any water present in the 

steam it would evaporate; if not, the steam, 
being at a temperature higher than the tabu- 
lar value for the pressure, is superheated. 

4. The temperature can be increased. The 
pressure will go up a little, since the steam 
acts like any gas receiving heat. As in case 3 
it is too hot for its pressure, or is by definition 
superheated. It can be cooled from this state 
without condensing, down to the condition 
of dry saturated steam, and condensation 
only sets in as in case 2, after the cooling 
down to the equilibrium point has taken place. 
In an engine operating on the most econom- 
ical principles in the use of steam (paragraf 
303), the final tempera- 
ture at the end of the 
piston-stroke is lower 
than at the beginning 
when steam entered from 
the boiler. Hence when 
new fresh steam comes 
from the boiler it finds 
itself exposed to the con- 
ditions of case 2, in con- 
tact with the piston and 
cylinder walls. Some 
Fig. 281. weight of steam is at once 

condensed to mist or to 
drops of water upon the metal. As the piston advances, the pressure 
falls after cut-off of the admission; then the condition of case 3 is 
present, and the mist or drops evaporate into gas, taking the heat neces- 
sary for this transformation from the walls or from the steam. All 
steam and water go out together as mist or gas when exhaust-valves 
are opened. This condensation and reevaporation is therefore twofold: 
" initial," due to cooler masses of metal, and secondly, that due to 
expansion and the doing of work. It explains part of the cause of 
missing water in the engine water-rate (paragraf 8). 





OWOFP 



BOILER PLANT AUXILIARIES 



323 



Drip 





Fig. 282. 



324 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



D) ^.SUJiFACE BLOW 



SU^FACE\BLO\Al-OFf^ 




,kS.COIMMT-Ct a^ifOlt 




Fig. 283. 



BOILER PLANT AUXILIARIES 



325 



329. Methods of Superheating. If the steam on its way from the 
disengagement area of the boiler (paragraf 48) which it leaves as wet 
steam or as dry saturated steam, according to circumstances, can be 
made to pass over or through an additional heating surface where it 
may undergo heating as in case 4, the initial condensation loss can be 




Fig. 284. 



prevented largely or wholly. The steam can be cooled enough to heat 
the metal to the steam temperature, and leave a margin of heat above 
that temperature at which condensation begins. 

This superheating can be effeoted in two ways. The steam can be 
passed through pipes in the combustion chamber of the boiler, so as to 
use heat which would otherwise be wasted. This is called indirect 
superheating: the other plan is to use a special furnace separately 
fired and for this purpose alone. This is called direct superheating. 
The rise of steam temperature above that of saturation of from 75° to 
150° F. is called low superheat; if from 150° to 225° it is medium super- 
heat; above 225° and rarely exceeding 300° will be called high super- 
heat. If the steam be at 150 pounds pressure, and a corresponding 
saturation temperature of 354°, the total temperatures will be from 
430° to 650°, which are so high as to give trouble in the directions to be 
referred to later in paragraf 231. 

Fig. 285 shows indirect systems of superheating where in a boiler of 
shell or sectional type an additional heating surface of pipe has been 
introduced to absorb heat otherwise wasted. Fig. 286 shows a direct 
system where the heat is derived from a special fire and grate. In the 
direct system there is better control of the degree of superheat and it can 
be higher than in the other system, where just in proportion as the boiler 
proper is well designed, there should be little excess of heat available 




Fig. 285. 



326 



BOILER PLANT AUXILIARIES 



327 



for superheating, and the temperature of the gases on leaving the 
heating surface should not exceed 600° (paragraf 107). Fig. 287 shows 
a locomotive superheater and reheater in the smoke box. 

Superheating has been considerably applied in the locomotive where 
the. conditions of use in the external air make the condensation losses 
excessive. The apparatus is introduced into the smoke-box and in one 
design certain of the upper tubes enlarged for the purpose. Tubes of 
one and one-fourth inches diameter lead from a header connected to the 
dry pipe in one design nearly back to the rear tube sheet and then 





Fig. 286. 

forward again to a second header leading the steam to the cylinders. 
In a test of these superheating coils, with 193 square feet of super- 
heating surface, a superheat of 122° was obtained when the boiler was 
evaporating 7 pounds of water per square foot of heating surface. At 
an evaporation rate of 15 pounds of water per square foot, the super- 
heat was 188°. In some boilers of coil or sectional type, superheating 
occurs in such part of the boiler as is exposed to heat of flame or 
gas above the water line, or beyond it (paragraf 100). 

330. Advantages of Superheating. The advantages of superheating 
the steam above the temperature of saturated steam at that pressure 
are 

1. A lowering of the steam consumption or water rate by lessening 



328 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

or eliminating the initial condensation in the cylinder from the relatively 
cooler piston cylinder head and side walls. 

2. A reduction in the amount of condensation during an expansion 
after cut-ofT. This is more surely attained by jacketing the cylinder 
and head with hot dry steam, but the heat to ehminate such condensa- 
tion during work is supplied from the heat of the jacket steam made 
by the fire, and condensation in the jackets should be charged to the 




Fig. 287, 



consumption within the cylinder also. If superheating is done by heat 
otherwise wasted, and the steam can be thoroughly dry when exhaust 
occurs, the expense of the jacket construction and its consumption have 
been saved to the fuel burned. Adding these together, an average 
economy of steam would appear to be represented in tests where the 
water or steam rate per I.H.P. was reduced by superheating from 24 
to 27 pounds to 20 to 22 pounds per hour. This is an economy or saving 
of 17 per cent. 

3. It is better to attack condensation by superheating than by the 
hot steam jacket, since the latter furnishes heat continuously, and 



BOILER PLANT AUXILIARIES 329 

must therefore be heating the exhaust steam on its way out and to 
waste. The cooUng takes place from the exhaust in any event, but the 
loss is less. 

4. The adjustment of the point of cut-off with saturated steam has 
to b'e earlier than with superheated steam, in order to secure the same 
water rate in order to offset the condensation loss. It is of advantage 
to reduce the degree of expansion to get equal distribution of piston 
effort. 

5. The superheating expands the volume of the steam for a given 
weight at any pressure. Hence the cylinder volumes can be increased 
in the later cylinders of multiple type and secure the same degree of 
expansion as with saturated steam. 

6. Due to this, the engine can be speeded up, since the lowered 
density or weight per cubic foot enables it 'to attain higher velocities 
through pipes and passages without throttling effect. This increase in 
velocity may be from 40 to 60 per cent. 

7. A cheaper engine or one with fewer cylinders can secure the same 
economy with superheated steam which is secured with saturated 
steam only with a continuous expansion in several cyhnders. The 
multi-stage expansion has for one of its objects the lowered tempera- 
ture rate of change due to the less pressure range in each cylinder. 

231. Disadvantages of Superheating. To secure the superheating, 
certain difficulties must be entailed. 

1. Deterioration and expense of maintenance of the superheating 
surface, exposed to high heat on one side, and only inadequately cooled 
upon the other. These metals oxidize, waste, and give trouble at the 
joints. 

2. Valves and their casings become deformed and leak, or by expan- 
sion of certain types, they stick. Corliss valves do not work at their 
best with superheats of over 120° or total temperatures of 500°. Poppet 
valves of two or even of four seats avoid the troubles from defective 
lubrication. Piston valves are the alternate type. 

3. Packing for the piston rod cannot be of the fibrous sort or contain 
rubber or any carbonizable material. Metallic packings of alloys 
resembling Babbitt metal — say 80 per cent antimony and 20 per cent 
tin — give best results. 

4. Lubrication cannot be done by mixing the oil with the incom- 
ing steam. The latter makes a gas of the oil and it produces little 
effect. The oil should be of the mineral or non-oxidizing class, and 
should be introduced mechanically by a pump into the cylinder and 
upon the rods and valves. Graphite in some flocculent form avoids 
these troubles. 



330 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

5. The castings of the engine must not be of comphcated form, 
liable to warp by heat. Prolonged exposure of cast iron in particular 
but also of all forms of iron to the temperatures of superheated steam 
causes them in time to grow permanently larger, due probably to some 
molecular rearrangement of the crystalline or other structure. 

6. The heat used to superheat the steam from an extra fuel supply 
must be charged to the fuel rate. The economy of superheating if 
stated in terms of fuel economy is usually less than when stated in 
terms of steam-consumption and water-rate. That is, a steam economy 
of 20 or even as high as 30 per cent will be cut down to an economy 
of 10 and 20 per cent in terms of fuel. 

7. The offset of advantage No. 7 is that in engines which have 
been bought and paid for, the economy of superheating is not as great 
in expensive multi-cylinder engines previously run on saturated steam 
as it will be in cheaper simple engines, non-condensing. 

It is not advisable to give capacities of superheaters within too 
close limits, since so many factors enter which would influence the 
computations in any given case. In a general way, however, about 
two square feet of heating surface go to each horse-power in indirect 
systems aiming to get 150° of superheat. 

The materials which resist heat best do not resist pressure equally 
well. Cast iron, which stands heat with slowest oxidation, is unreliable 
by itself. Hence an ingenious combination has been made of cast 
iron washers forming flanges which are shpped on and shrunk over 
a steel pipe. The flanges become red hot and conduct heat to the 
inner tube while protecting the latter. The steam is led in a thin 
film along the superheating surface by the use of an inner tube which 
acts as a displacer or filler of the center of the main tube. The other 
features of successful design must be adequate support to prevent 
deformation by the weight of the superheating coil in case of high heat; 
accessibility for renewal or repair; free expansion under varying heats. 
To save the superheating surface when the engine is not running and 
steam is not circulating, some designers have arranged to have the 
superheater flooded at such times. This is objectionable from the 
care which is required when the superheater is to be started anew, 
lest the engine get the water in objectionable amounts. It also gives 
trouble from scale therein. 

333. Combustion Indicators. There should also be included under 
auxiliaries of the boiler-plant as apparatus but not as machinery the 
means used to inspect and control the effectiveness of the combustion 
in the furnaces. The complete laboratory equipment for volumetric 
analysis of the products of combustion is known as the Orsat apparatus, 



BOILER PLANT AUXILIARIES 



331 




Fig. 290. 



332 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

and includes three vessels for the absorption of carbonic acid gas (CO2), 
carbonic oxide gas (CO), and oxgyen. This has been fully described 
elsewhere * and depends on the successive withdrawal from a given 
volume of gas of the foregoing elements, measuring the resulting volume 
after each element has been withdrawn. For practical use and guidance 
of the fireman, a simpler and continuous apparatus with a recording 
apparatus has been successfully devised in Germany and America, in 
which only the percentage of CO2 is recorded by a curve, on the ground 
that if the CO2 is kept high, the other losses in excess of oxygen due 
to holes in the fire and from incomplete combustion to CO due to too 
little air, will be kept low. The hydrogen in the fuel is sure to burn 
to H2O. If the fuel is low in hydrogen, and be called carbon, and is 
burned with a dilution of air of 100 per cent excess, the maximum 
carbonic acid will be about 14 per cent of the products of combustion. 
For the proportion of CO2 in theoretically perfect combustion with 
just enough air is 3.66 pounds of CO2 in 12.3 pounds of CO2 and nitrogen 
mixture in the products of combustion, or the CO2 is 29.7 per cent by 
weight. If double the weight of air is added, for air over the fire, 
then the products should have CO2 in the proportion of 3.66 to 26.26, 
or at 13.9 for each unit weight of coal. Too little CO2 in the chimney 
gases in the volume of the sample indicates excesses of air from leakage 
through holes in the fire, or through the setting: or if smoke is also 
present to the eye, that the carbon monoxide is in excess. Usually the 
oxygen or free air is in excess when the draft is powerful. Fig. 290 
shows the apparatus used in one of these CO2 recorders which has 
had widespread acceptance. The chimney gas is drawn in at Q by a 
water-injector: the caustic potash absorber of CO2 is in the vessel A; 
the sealed bell A^ receives the unabsorbed gas under determined 
pressure and determines the height traced by the pen Y upon the 
chart driven by the clock mechanism in 0. Then the tubes are 
scavenged by siphoning action of the water, and a new charge of fresh 
gas is drawn in and sampled. The flow of water through the cock S 
determines the frequency of the sampling and recording process. The 
fireman or others interested can inspect the curve of the chart and 
see exactly what needs to be done. At the 59th Street power house 
of the Interborough subway system of New York City, an economy 
was effected in reducing the stack loss of 22.7 per cent by 19 per cent 
of itself in hand-firing conditions, and with stoker firing of 12 per cent. 
333. Water-meters. The equipment of measuring apparatus to give 
the water consumption of the plant is an important auxihary. If 
the water must be paid for per unit used, the meters are a check upon 
* " The Gas Engine," F. R. Hutton, p. 103, John Wiley & Sons, 1908. 



BOILER PLANT AUXILIARIES 333 

waste. Increase in the water rate above the normal or standard con- 
sumption indicates some disarrangement or mal-adjustment; and every 
pound of water unnecessarily fed to the boilers means so much extra 
coal burned to evaporate it. 

Self-registering or recording water-meters are therefore the most con- 
venient and satisfactory; but if by reason of their cost they are not 
realizable, the records of the common type can easily be plotted from 
their readings. 

Water-meters are of two classes : the shunt form, where only a part of 
the water passes through the meter, and the holotype class, in which all 
the water used goes through the meter. The objection to the first type 
is the uncertainty whether the water passing the meter is actually the 

computed fraction - of what passes in both the main pipe and through 

the shunt or by-pass. The advantages are the smaller size and cost of 
the meter and the fact that the disarrangement of the latter does not 
stop the flow in the larger cross-sections. 

Water-meters are positive or displacement instruments; or they are 
velocity indicators or recorders. The displacement type are in effect 
piston or plunger water-motors, whose piston strokes empty and fill a 
known volume at each reciprocation. The water temperature remaining 
constant, and the pistons having no leakage from wear, such meters 
should be closely accurate. The recording mechanism registers the 
number of strokes, which can be read in cubic feet and gallons when the 
displacement volume is accurately known. They usually cannot go at 
very high speed, and for large cross-sections are bulky and heavy. The 
velocity meters of small capacity have a propeller wheel which is turned 
by the flowing current of water. The speed of such revolution recorded 
by a counting mechanism gives the lineal rate of flow, and this multi- 
plied by the cross-section gives the volume. Friction is the bane of such 
meters, retarding and rendering variable the response of the wheel to 
the real velocity of the water. Both types require strainers to keep 
grit and mechanical obstacles from the measuring chamber. 

The Venturi-meter which has no moving elements or mechanical 
details, is the best water-meter for large cross-sections, and for very large 
pipes and considerable velocities of flow is the only possible or practicable 
one. Its principle is a theorem of Bernouilli. 

Let a pipe of circular section have two cross-sections of differing areas in a section 
of limited length. The section should be made tapering from the larger area a^ to 
the smaller section or gorge whose area is a.^, and then gradually be increased again 
to the full original size a^. Let there be inserted in the pipe a pressure-measuring 
or observing apparatus such as a gauge or manometer at the point where a, is observed 
and another at the smallest section or throat. Let the head at a^ be called A, and 



334 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

the head at a^ be h^. Then, since the quantity Q in cubic feet of water passing in 
the pipe per second is the product of the area in square feet into the hnear velocity 
in feet, and since water is incompressible, it will be true that 

Q = AV= a{v^ = a^v^ (1) 

where Vj and V2 are the respective velocities at a^ and Og. 

But the incompressibility of the water and the consequent velocity variations at 
Oj and flg will make the heads of pressure at these points to differ so that the relation 
will hold 

whence 

v,^ - v,^ = (h^- h,) 2g. (3) 

From equations 1 and 2 may be written 

b' = (1)1 - b' =(1)1 = 2 i' (ft. - '•^). (4) 

whence 

But since the areas a^ and a^ are constant and known, the fraction in the above 
equation can be computed once for all and multiplied by the \/2 g; if this quantity 
be called K, then 

Q = KV h,- h,° (6) 

From the readings of the pressures at a^and a^the quantity flowing can be known. 
If the two gauges be so connected that the reading observed or recorded is the 
difference hi — hi = h^, then the quantity is Q = K\/J[~ ' 

234. Concluding Comment. It may easily happen that auxiharies 
listed in the later chapter under engine-room auxiliaries will be 
located in the boiler room of a particular plant. This will be done 
for convenience and the logic of its location there will be entirely 
defensible. But the more usual attachment of these to the engine 
economy and efficiency and the advantage of familiarity with the 
engine before discussing them are reasons for placing them in the 
second group (paragraf 21). The pumps and the forced-draft 
machinery are also called auxiliaries in general speech and in the 
accounting of the plant, but by the logic of Fig. 1 and the method 
of treatment these have been called essentials as they are, in fact, in 
themselves or in alternate form. Certain topics also concerning the 
plant as a whole, the testing for economy and efficiency of the boiler 
plant, and the economic questions are reserved also for later treatment 
after the engine plant has been made familiar. 

The energy of the fuel having been liberated in the furnace and trans- 
formed into pressure of steam gas is now to be transmitted through 
piping to the engine mechanism which is to make it available in mechan- 
ical form. 



PAET IV. 



CHAPTER XIV. 

THE PIPING OF PRESSURE TO THE ENGINE AND ITS ACCESSORIES. 

335. General. It is usual in important power-plants to isolate the 
engine from the boiler plant in a separate room or in a separate structure. 
The reasons for this include: 

1. Better insurance rate by concentrating the fire and explosion risk. 

2. Avoidance of injury to costly machinery from the gases and dust 
of the fire-room. 

3. The higher standard of maintenance and upkeep of the machinery 
favored by such separation than is possible or worth while in the firing 
room. 

4. Convenient development of each department by adding units, 
without interference. 

5. The separation of the differing grades of service. 

6. The easier differentiating of the accounting, where the generation 
of power and its consumption are separate. 

There will doubtless be other reasons of weight in special cases. 

It will be apparent, therefore, that the pipe which conveys energy in 
the form of pressure from the boiler and grate where it has been liberated 
and stored is as essential and vital a link in the chain of power produc- 
tion as either the boiler plant or the engine plant. Its disablement 
or breakdown btops the industry or productive processes dependent 
upon the power of the engine as completely as the annihilation of the 
boilers or the wreckage of the engine. If the financial loss or personal 
discomfort of those dependent on the continuity of the plant's working 
are sufficient, the designer may well expend thought and money upon 
the engineering of his transmitting pipe. 

In small plants such as a portable contractor's outfit, which is none 
the less a complete plant, the problem may be simple and inconsiderable. 
In larger installations both pipe and necessary fittings become costly, 
and time for repairs increases with the sizes of the units, making such 
upkeep both costly and an economic loss as well from the loss of salable 

335 



336 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

product. Sometimes such loss from a shut-down far outweighs in two 
days the entire additional first cost of a more elaborate and more care- 
fully installed proposition. 

336. The Stresses in a Steam Pipe and its Requirements. The stresses 
to be resisted and the difficulties to be avoided or reduced to their least 
values in the design of a pipe system include: 

1. Internal static pressure from the steam tending to rupture it along 
the cylinder elements. This pressure is Pd as in the boiler, and is 
resisted by 2 tf (paragrafs 24 and 25). 

2. Internal static pressure from the steam tending to pull it apart at 

the joints. This pressure is P;r — as on the head of a cylindrical boiler 

and is resisted by the flange-bolts, or the threads of the screws at the 
ends of the pipe-lengths, and by the greater strength of the pipe 
ringwise, measured by ndtf. Failure of good pipe in the body 
of the material from this stress is unknown. The joints always fail 
first. 

3. The static tension lengthwise of the pipe due to its expansion by 
heat of the steam within it. If the pipe was put up cold, or at 65° F., 
and when at work is exposed to steam of 150 pounds pressure whose 
temperature is 365° F., the steel of such pipe will be longer when hot by 
.00000689 of itself per degree per unit of length. If the length be 100 
feet and the temperature rise 300 degrees, the increase in length will be 
0.21 of one foot or two and one-half inches in that length. The force 
exerted by this heat change is measured by the completeness of the 
anchorage of the pipe to any fixed object. If the fixation is complete, it 
is ndtf, or the tensile strength of the hollow cylinder whose thickness is 
t and whose diameter is d, in pulling, and the compressive or buckling 
resistance of such a column if it is pushing. Expansion should not be 
resisted, but should take place freely without pushing or pulhng any 
anchorage or tearing apart any joints. 

4. A dynamic stress of unknown and scarcely calculable inten- 
sity (the quantities being unknown) resulting from a water-hammer 
phenomenon in the pipe. When by condensation of steam to water 
which is not removed by drainage a mass of condensed but hot water 
under pressure gathers in a pocket or recess in the pipe during a period 
of arrested or retarded flow of steam, there is great danger on a rees- 
tablishment of flow that this water will be picked up bodily by the 
rapid flow of steam gas over it. By its inertia and mass it will resist 
diversion of its direction of flow by elbows or tees, but will be brought 
up against such fittings with a blow whose intensity is measured by the 
mass of water multiplied by its velocity. If the mass is large enough, 



i 



PIPING OF PRESSURE TO ENGINE AND ACCESSORIES 337 

and moving fast enough, it has force enough in that blow to crack 
fittings or break them into pieces if of brittle material, or to split the 
pipe lengthwise. The noise of such blow is alarming and when con- 
tinuous becomes impossible to endure. Water hammer may also occur 
in the warming-up process. Condensed water gradually rising in tem- 
perature in pockets of the pipe as hot steam flows to it from the boiler 
reaches the critical temperature at which it is ready to flash into steam 
at any lower temperature than that of the steam pressing upon its 
surface. The opening of a valve or any sudden cooling beyond the 
water pocket causes a rush of steam towards the lower pressure which is 
not met from the boiler by reason of friction in the pipe. The heated 
water changing suddenly and in part into steam explodes the water 
pocket as it w^ere, carrying the unevaporated water with it and causing 
the water-hammer disaster if the masses are large enough. This 
phenomenon is the same as the '^ concussive ebullition " alleged to be a 
danger in the boiler itself. The only way to prevent this disaster is 
adequate drainage of all pockets, so that there can be no water accumu- 
lations in the pipe at all. The pipe cannot be made strong enough of 
itself. 

5. A thermal loss of heat and pressure by radiation to the air around 
the pipe, increasing the amount of the condensed water above, and by 
friction in the pipe making the pressure at the engine less than that at 
the boiler. This drop of pressure is reduced by effective non-conducting 
coverings surrounding the pipe. 

6. A frictional loss from resistance to flow in the straight lengths of 
varying cross-section, and at the bonds, outlets and controlling valves. 
Such loss appears as a difference between the initial pressure at the 
boiler, p^, and the resulting terminal pressure at the end of the pipe, p,- 
This difference p^ — p., will obviously vary directly as the length of the 
pipe in feet L; as the density or weight per cubic foot of the steam at 
the initial pressure p, since this is in effect the moving force which keeps 
the contents of the pipe in motion, or is equivalent to a pressure head 
in a hydrauHc problem: since the quantity of matter undergoing the 
retardation is the cubic feet of steam per minute Q multiplied by uo. 
The loss will vary inversely as the diameter d in inches in some power, 
and will vary also as that diameter multiplied by a coefficient to take 
account of experimental data that the loss of head is proportionally 
greater in small pipes than in large ones. One of the most widely 
accepted formulae for flow in pipes is D'Arcy's, which takes the form 

Q'wL 



338 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 
from which 



or, since 



wL 
W = Qw, 



If the D'Arcy coefficients be introduced for c the values of c corres- 
ponding to each d must be taken from such a table as Table XII. 



TABLE XIL 

COEFFICIENTS FOR RESISTANCE TO FLOW IN PIPES. 



For diameter d in 
inches 


i 

36.8 


1 
45.3 


2 
52.7 


3 

56.1 


4 

57.8 


5 

58.4 


6 
59.5 


7 
60.1 


8 


Corresponding value 
f or c is 


60.7 


For diameter d in 
inches . . . 


9 
61.2 


10 

61.8 


12 

62.1 


14 
62.3 


16 
62.6 


18 
62.7 


20 

62.9 


22 
63.2 


24 


Corresponding value 
for c is 


63.2 



A more usual avenue of approach to the problem for steam is by an 
assumption of a linear permitted velocity in feet through the pipe. 
Such velocity in feet per minute V will be 



V = 



Q XTZtP 

4 X 144 



and experience shows that 100 feet per second or 6000 feet per minute 
is not too high so as to cause excessive resistance or loss of head on the 
one hand, or make so large a pipe as to be of prohibitory cost on the 
other. For example if the gage-pressure be taken at 100 pounds and 
the value of w found to be 0.264 pounds and L be called 100 feet, then 



d 



8.8 



P1-P2 



This means that a 9-inch pipe (or 8.8-inch) 100 feet long carrying 100 
pounds pressure would lose one pound of pressure: or, that a one-inch 
pipe would lose 8.8 pounds. These values are within the limits of 
good judgment. 



PIPING OF PRESSURE TO ENGINE AND ACCESSORIES 



339 



7. A final requirement is that the hollow pipe cylinder considered as 
a girder, having a wall-thickness as determined by (1) and a diameter 
determined by (6), carrying its own weight, and that of contained water 
if any, and the weight of non-conducting covering added so as to meet 
(5) shall not flex between its supports enough to bring an extreme fiber 
stress on the elements of the pipe itself, and, even more important, that 
there be no tendency to open the joints. The pipe is therefore in the 
condition of a continuous girder resting upon many supports and 
uniformly loaded or nearly so. Heavy valves make a concentrated 
load on the two adjacent supports, but the load is fixed, and its effect 
should not go beyond them. This is a problem of the supports rather, 
than of the pipe. 

337. The Material for a Steam Pipe. There will be four standards 
in the engineering of steam lines. High-pressure work — say above 
150 pounds pressure — and low pressure work and exhaust piping form 
two of these, and the other two are large diameter work — say over 6 
inches diameter, — and small work. In small work the engine builder 
often fixes the steam-pipe size by the steam inlet into the cyhnder. 
Knowing the cylinder volume and the proposed number of traverses 
per minute, the total steam volume is found: this volume divided by 
the limit of 6000 gives the pipe area and hence the diameter in feet or 
fractions of a foot. 

For small diameters and low pressures the standard lap-welded steel 
pipe is safe enough. This can be bought up to eighteen inches in 
diameter without extra price in standard sixteen-foot lengths. It has 
been tested up to 2000 pounds pressure for its weld but should not be 
used at one-tenth of this. For higher pressures and smaller diameters, 
the extra heavy or hydraulic pipe will be spe- 
cified, the greater thickness giving better and 
more reliable welds. For larger diameters and 
medium and high pressures the pipe will be 
of riveted steel plate (Fig. 291), lap- or butt- 
riveted on the longitudinal seam, and flanged 
and welded or riveted by hand or power at 
the ends where the joints are to be made. 
Spiral welded pipe has not come into general 
use for heavy work in spite of the advantages 
of long length of its units. Spiral riveted 
pipe for light work and exhaust pipe is much 
used (paragraf 245 and Fig. 331). Cast iron 

is not reliable for high-pressure work by reason of the high modulus 
of elasticity, and its relatively low tensile strength. This makes 




Fig. 291. 



340 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

the pipe thick and heavy, and it should not be exposed to stresses 
of unequal temperature and cross-bending. Cast-iron fittings will 
still be used for joints and branches and for valve-bodies, even 
where steel is used in the run of the pipe. Drawn steel or alloy 
tubes are used in high-priced small diameter work for heavy pres- 
sures, since there is no weld in such pipe as it is drawn down over a 
mandrel from a solid cast ingot of proper weight and shape. Copper 
pipe has been used in marine practice where pressures were not great, 
because it could be curved so readily with gentle sweeps to get round 
deck-beams and past corners in contracted space. Such pipe was 
made for light work by taking sheet copper, bending it into a cylinder 
over a former and brazing the longitudinal joint, using brass filings as 
the solder. The joints were made by brazing flanges on the pipe. The 
next stronger stage was the use of electro-deposited copper, deposited 
on a former or core until the desired thickness was reached. The pipe 
was then hammered and annealed to secure ductility and homogen-eity. 
The third step has been to wind a copper pipe with steel-wire outside of 
it to give the strength of the steel while retaining the ductility and 
flexibility for curving. After the winding, the reinforced pipe could be 
again placed in the electro-plating bath and an exterior shield of copper 
deposited outside the reinforcing wire. Copper has much less strength 
than steel but expands and contracts easily without injury to itself and 
resists corrosion. 

The modern tendency toward higher pressures and their economies 
compels the pipe to be made like the steam and water drums of the 
sectional boilers, and to follow the lines of their practice in butt-riveted 
joints and the use of high-class steel of specified quality (paragraf 26). 
Cast steel is not much used except in fittings. 

338. Steam-pipe Joints and Fittings. The inconveniences of manu- 
facture and shipment of extra long single lengths of pipe usually make 
such units costly to buy. Twelve-, sixteen- and twenty-foot lengths will 
be the usual standard. How shall the successive lengths be joined 
together strong and tight? In small-diameter low-pressure work the 
end of the pipe will have a thread cut into the metal of the pipe by a 
die or threading machine. Such thread will have a taper of one in 
sixteen or three-quarters of an inch to the foot, and for a length sufficient 
to get six or eight of the threads of such a screw into a corresponding 
female thread upon the next element in the line. By screwing up until 
the thread refuses to enter further under the compulsion of a pipe- 
wrench of sufficient leverage the joint is presumably tight as weU as 
strong when both threads are standard. Such threads, however, being 
incised, leave the pipe-metal thinner at the bottoms of the threads than 



PIPING OF PRESSURE TO ENGINE AND ACCESSORIES 



341 



elsewhere and therefore the stretch lengthwise clue to heat and pressure 
will be concentrated at these threads. The stretching loosens any scale 
of sesquioxide of iron which may have formed, and the pipe corrodes 
more rapidly here than elsewhere, and then the joint leaks under the 
thread. 

If the threads are right-handed, or make up by screwing the turned 
element in the direction of clock-hands, the closing of the last joint 
between fixed objects like an engine and boiler is a problem. The 
introduction of a left-hand screw is one solution but is not used above 
2-inch pipe. The union is the more satisfactory device (Fig. 292), 
giving a closing nut with a female thread at one end, and with a finished 
sliding contact surface internal to its other face. These make up on 
special fittings screwed on the pipe at the two ends to be joined. No 
springing of the pipe lengthwise is necessary with the union to get the 







'^/M 


K_ 




f^ 


i^M 


llf£"---"i 


— 


y 




:.-.TT7T7-.-:r/ 








Fig. 292. 



Fig. 293. 



two threads into the closing fitting as with the right-and-left screw,, 
and no difficulties appear from unequal entry of the two threads into 
such fitting, whereby one thread refuses to go further while the other 
is not yet tight in place. The contact faces of the two union elements 
exposed to pressure and leakage are best ground surfaces; where this 
is not desired some compressible material of soft metal or fiber or rubber 
composition must be introduced as a gasket. New designs show an 
inserted contact ring of brass or alloy on the hollow face. The friction 
of large union nuts, and the difficulties of getting adequate strength 
even with malleable iron have kept these down to smaller sizes. The 
machine work on them makes them costly. Hence the flange joint will 
be used in all important work. 

Fig. 293 shows a typical pair of flanges with the pipe ends screwed 
into them. The faces are bolted together with a gasket between, 
either of flat soft metal or of fiber or of manufactured composition 
with rubber and graphite or asbestos as probable elements. Corru- 
gated or ribbed gaskets of copper or soft metal have wide acceptance. 



3i2 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



either plain or in combination with fiber or special material as in Figs. 
294 and 295. The two halves of the flange are made up by putting 
a couple of taper steel pins into the bolt holes on opposite ends of a 
diameter, and then by a steel bar bearing against the sides of the 





Fig. 294. 



Fig. 295. 



projecting pins on the face, the threads are made up to refusal. In 
Fig. 295 a special metal face is used, w^hich can be ground. To im- 
prove the permanence and quality of the screwed flange joint, a 
number of modifications of the type of Fig. 292 have been made and 
have worked well. 

1. To run the pipe through the flange until it projects beyond the 
face by a sixteenth of an inch, and then face the projecting end and 
face off in a lathe. 

2. To form a recess in the face at the end of the threads, and to upset 
the end of the pipe by hammer-peening 

down into this recess, and face off in the 
lathe. 

3. To form a projecting ring on the face 
of one flange, which fits into a correspond- 
ing annular groo've in the other face (Fig. 
296). The same purpose is secured by 
raising a part of one face and depressing 
an area of the same center and diameter 
upon the other, so that they shall interlock. 

These both are to lessen the stress upon a soft or non-metallic 
gasket to blow it out radially (Fig. 297). The interlocking, while tend- 
ing to preserve alignment, is yet open to the objection that when a 
gasket is to be replaced or any repair to the joint is required in heavy 
pipe systems, a jack must be used to spring the joint open after the 
bolts have been released. 





Fig. 296. 



Fig. 297. 



f 



PIPING OF PRESSURE TO ENGINE AND ACCESSORIES 343 




Fig. 298. 



The more recent development of the flange joint has been towards 
the " loose flange " principle in which the faced joint-forming elements 

are not fast upon the lengths of pipe. In 
Fig. 295 is shown the type in which the pipe 
is screwed into a special end-fitting, and the 
two halves are drawn together by the loose 
flange bearing against a shoulder on the fit- 
ting. This is a derivative of the union, and 
is, in fact, a bolted union. In Figs. 298 
and 299 are the loose flange types, American 
and British, in which the end of the pipe 
section is flanged over after the half flange 
has been shpped over the end. The contact is thus made with the pipe 
ends and the flange bolts draw them close and collars or recesses in the 
flange cover in the radial joint in the British 
forms. 

Again the pipe may be expanded into the 
metal of the flange as a boiler tube is ex- 
panded into a tube-sheet (paragraf 57). Or 
finally the end of the pipe is flanged over 
and then welded to a flange ring of sufficient 
thickness to make a strong and stiff perma- 
nent joint. This is an admirable but costly 
way, and if anything happens to the integrity 

of the faces the whole pipe section must come down and be taken to the 
forge and shop (Figs. 300, 301). Fig. 302 shows welded nozzles with 

flanges, and heavy flange joints. Fig. 301 
is what is cafled the Van Stone joint, with 
pipe end thickened first, then flanged over. 
The thickening is effected by a welded ring. 
Pipe-fittings include all special devices for 
connecting pipe and permitting branch out- 
lets to be taken off at angles. In small 
work these will be screwed on the outside 
of the male thread on the pipe: in larger 
work flange joints with bolts will be 
used. In small work these fittings will be of cast or malleable 
iron: in larger of steel castings. In small work the branch may be 
taken off at 90° from the main stem, or the corner be turned with a 
90° elbow: in large work the angle will be changed to 45° or the curve 
produced by a long pipe sweep curved while hot to an arc of several feet 
radius and always over five diameters of the pipe. The tee for a 




Fig. 299. 




Fig. 300. 



344 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



r^ ^\ ^ 



D+'^ii 



^ Reinforced with 

welded "band 



I 




^ 







:i 



-.1 



Tor more 



TV 



•\ / 



Pipe finished after 
\ vanstoning to fit flanga 

Flange bored 



Fig. 301. 




Fig. 302. 



PIPING OF PRESSURE TO ENGINE AND ACCESSORIES 



345 



-tt- 


S' 


*". 1 


! 1 



f 



-M-4. 




^ F- j^ 



£ 



I 









£ 



:5 



right angled branch in small work becomes the Y when the branch 
starts at 45°. Fig. 303 shows the standard types of fittings, with short 
and long radii, and outlets at 90° and 45°. The proportions given by 

the letters vary slightly 
with different makers, 
but are always furnished 
by them in their lists. 
Recent practice and par- 
ticularly with super- 
heated steam has favored 
the replacing of tees by 
welded nozzles formed on 
the pipe itself (Fig. 298), 
lessening the number of 
joints to give trouble and 
the time to erect the pipe 
but at the expense of 
first cost. 

339. Expansion of the 
Steam Pipe by Heat. 
Since the force which 
expands a steam pipe 
by heat from within 
is practically irresistible 
(paragraf 231), the best plan is to let it take place freely, but control 
the direction and starting points of such expansion. It is very undesir- 
able to have such expansion produce cross-strains on fittings or tend 
to open joints. The pipe may be 
anchored at one end and expand 
toward the other: or it may be 
anchored in the middle and expand 
both ways. It cannot be anchoied 
at both ends: it will either buckle 
and set its joints to leaking, or it 
will push or pull over one or both 
of the anchorages. 

In small work with light pipe, 
the loop of Fig. 304 has been much 
used, either in copper formerly or 
in steel latterly. The bending is 
not enough to go beyond the elastic limit in the extreme fibers. The 
same result is better attained by the rectangular offset to a parallel 



ELBOWS 



TEES 



Fig. 303. 



CROSSES & 45' 




Fig. 304. 



346 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



vertical plane as in Fig. 305. Expansion spends itself in twisting the 
two vertical riser nipples, and in changing the direction of the center 
line BC and its angle between the axes of the two pipes A and C. The 
length of the verticals should be long enough to allow for this torsion 



.1 






C 



o 

Fig. 305. 

without starting the threads in the elbows if screwed fittings are used. 
This can be worked also in a pair of horizontal planes, and advantage can 
be taken of a sudden change of level to introduce this type of provision 
or expansion. 

A third type is the slip joint (Fig. 306), providing that the two lengths 




Fig. 306. 



may bring their ends together or separate. One length, usually 
the comparatively fixed one, carries a stuffing-box with gland, and 
the other end a brass sleeve which slides steam-tight in and out of the 
stuffing-box as the pipe expands or contracts. These slip-joints are 
troublesome from leakage when the packing deteriorates, and from 
a tendency to seize and become hard and fast from corrosion and 
defective alignment of the pipe. Care must be taken also that the 
pipe is not allowed freedom of movement sufficient to blow the slip- 
tube out of the stuffing-box from end pressure of steam within the 
pipe. 



PIPING OF PRESSURE TO ENGINE AND ACCESSORIES 347 



To prevent this, the balanced type of sUp-joint has been made 
(Fig. 307), in which the sHp-tube carries an annular flange exposed to 
steam pressure and of an area equal to that of the pipe. Hence the 

tube is forced inward with the same 
pressure as the end to which it is 
attached is forced outward. The 
flange is also a mechanical stop trans- 
ferring pressure to the holding bolts 
which are not present in Fig. 306. 
In Fig. 308 the leaking sUp-tube is 
replaced by the corrugated copper or 
steel or alloy which is long enough 
to allow motions of the flanges towards each other or away without 
producing excessive flexure in any one groove. 

A fourth form is used for high pressures and temperatures and consists 
in making a flexible flange-joint of steel plate or of copper of wide 
diameter. The pipe is expanded into the middle of this flange and the 
two edges are bolted or riveted together ringwise. The flange opens and 




Fig. 307. 




Fig. 308. 



closes hke a bellows under changes of length (Fig. 309). This same 
type of expansion-joint is used in river-boat engines to connect the 
side pipes to the upper steam-chest, which is a part of the cyhnder- 
casting. 

240. Hangers and Carriers for Steam Pipe. The changes of length 
and motion of the pipe under heat must be provided for in arranging 
to support the weight of the pipe. It is best to have two points of 
support in each length between joints: then no bending or flexure 
comes upon such joints if properly alined, and erection of the pipe in 
place is made easy. The best way if there is head-room enough over- 
head is to hang the pipe by pendant^ rods from the girders or from 
brackets above it, with length of rod sufl&cient to allow for the come 
and go of the pipe. If there is little head room, then roller hangers 
of the type of Fig. 310 have been used in mills with wooden beams, 



348 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



/ 



or the type of Fig. 311 is standard for bracket supports in tunnels 
or upon side walls. There must be no tendency for the pipe to cramp in 
its lengthwise motion. 

341. Valves for Steam Pipe. In the simple and elementary power- 
plant of Fig. 1 there must be a valve in the pipe between boiler and 
engine to control or arrest the flow of pressure energy from the former 
to the latter. When the number of boilers and engines multiplies, 
the valves required to enable any boiler to be cut out for repairs or 
inspection increase proportionately. When the engines or boilers or 
piping are any or all of them in duplicate as a precaution against shut- 
down of the plant the valve system becomes complicated and costly, 
and yet each valve is again a vital unit, which must not be liable to 
fail at a critical moment. 

The valve which throttles the flow of steam from a single boiler 

to a single engine as in Fig. 1 will 
be called a " throttle- valve ". Any 
valve between boiler and engine 
performs this same function in a 
complicated system, but in this case 
f^ss-^^w^ssmssssmsssssy the valve which is placed close to the 
valve chest of the engine and serves 
to isolate that engine from the 
piping system is called its throttle- 
valve. These are often special re- 
specting outlets or length of stem, 
and are supplied with the engine 
itself. The rest are standard, and 
are bought with the pipe. The 
throttle-valve' of the locomotive is 
required to be quick-acting, particu- 
larly as respects closing; and the engineer is always standing by close 
to it. Hence it is quite usually of the balanced poppet type, with two 
disks on a common lifting stem with equal pressure below and above. 
In low-pressure work the throttle is often a disk- valve, swinging on an 
axis through a diameter of the disk, securing balance as in the damper 
of Fig. 193 or 194, and quick-action. But both the disk and poppet 
type require to be locked from undesired change of position, and for 
high pressures the advantage of the power of a screw movement and 
its property of self-locking in place have given screw-valves the 
preference. The disk-valve is also liable to inconvenient deformation 
by heat and pressure. 

As in the matter of the pipe itself, the valves will fall into groups by 



] [ 
] [ 



Fig. 309. 



i 



PIPING OF PRESSURE TO ENGINE AND ACCESSORIES 349 



sizes and by pressures. For small work and for all-round use with light 
pressures, the globe-valve of Fig. 312 will be found in the lead. The 




seat is in the plane of the axis of pipe and body, with a partition above 
and below to compel the steam to pass through the round hole in the 




A 



^^ 





Fig. 311. 



seat. The valve is conical on its face in small sizes, flat in the larger. 
Special metal or alloy disks or rings are used in the valve face or on the 



350 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



C 



xm 



:) 




Fig. 312. 



seat face or both, so that these can be renewed on wear without disturb- 
ing the globular body made up on the pipe. The spindle works on a 
square-threaded screw in a removable cap which 
carries also the stuffing-box. The cap when 
removed takes valve and spindle out for repair. 
The screw is universally right-handed in globe- 
valves, so that the valve is closed by a clock- 
wise motion of its wheel, and opened by 
reverse motion. The objection to the globe- 
valve is its tortuous passage with the pocket 
below the seat where water will gather in hori- 
zontal runs of pipe, and give chance for the 
water-hammer dangers of paragraf 231. Scale 
and sediment may also accumulate either above 
or below the seat, causing trouble in opening 
or closing. The trouble from water can be 
minimized by putting the valve with its 

spindle in the horizontal plane of the axis of the pipe, instead 

of vertically as in Fig. 313. 

Such valves also should be 

put with the bottom or 

lower face of the valve 

toward the pressure to be 

resisted, both because the 

packing of the valve can 

be renewed when pressure is on the line by the closure of the valve, 
and because if the seat or disk becomes de- 

^ "^ ^ tached from the spindle, the valve remains held 

down by the pressure if the latter is on top, 
and no indication is given of the inoperative 
state of the valve. 

In addition, the globe-valve becomes of 
inconvenient size and weight in large sizes of 
pipe if it is to offer anything like the opening 
of the pipe area itself. Hence straightway 
valves are preferred for large work. The 
globe-valve in the form of an angle-valve is a 
convenient and excellent type where it can 
perform the double service of the turn of the 
corner and the regulation of pressure (Fig. 
314). There is no tortuousness of passage, 

and can be no accumulation below the seat. The angle-valve is 




i^[3^ 



Fig. 313. 




Fig. 314. 



PIPING OF PRESSURE TO ENGINE AND ACCESSORIES 



351 



at its best with a vertical spindle and as before with the pressure 
on the under face. 

The straightway-valve is usualty of the gate-valve type. Such 
valves have the opening through them coincident with the pipe-axis, 
and the closure is effected by sliding a door or gate across the opening 
from one side, or from above. Since the gate has to resist pressure 
over its area and must be tight against this pressure, which strives to 
force it away from the seat, it is usual to give the valve a wedging 
action as it reaches its closed position, using the face of the opposite 
opening as the abutment for such force. This is done in two general 





Fig. 315. 



Fig. 316. 



ways: either by inclining the faces of the seats toward each other 
(Fig. 315) or b}^ keeping the faces of the gate parallel and separating 
them by a wedging effect of inchned planes between the backs of the 
two face plates of the valve, which are carried down by the spindle 
motion after the valve faces have reached their final vertical position. 
The advantage of this last principle is that the contact faces do not 
move over each other laterally after they have received nearly the full 
pressure required to close the valve tight, as is the case with the solid 
gate construction. In opening, the reverse action takes place, as the 
wedges or inclined surfaces release first, letting go contact with the faces. 



352 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 





U-i 



The loose faces rattle under certain conditions, and the other con- 
struction is cheaper. Gate- valves require a lateral recess into which 
the gate may recede and leave the thoroughfare through the valve wide 
open. The spindle may work in a screw formed in the 

Tjj^ gate, to move the latter in and out (Fig. 316). The 

^^ screw is then altogether inside the case, and the stem 

is called a " non-advancing stem." There is nothing 
external to indicate by position of wheel or stem 
whether the valve is open or closed, but the stuffing- 
box does not have the spindle working spirall}^ through 
and keeps tighter. If the thread on the gate and 
spindle is made right-handed, the valve is opened by 
clockwise turns of the wheel, which is the motion to 
close an " advancing " stem-valve when the nut threads 
are a part of the valve casing and not of the valve gate 
(Fig, 315). Hence it is desirable, to prevent confusion 
and error, to put an arrow on the 
rim of the wheel and the word 
^' open " to indicate the direction 
to turn the wheel to open. An 
increasing favor attaches to the 
outside screw-valve of Fig. 315. 
The nut threads are here in the 
hand-wheel, outside, the stuffing- 
box, and held from end-motion by 
a yoke. The stem is held from 
turning from its connection with 
the gate, but '' advances " as the 
gate is lifted from its closed posi- 
tion. As before right-hand threads 
on the stem will make the valve 
open by clockwise motion of the 
wheel and close by anti-clockwise turning. Arrow and word should 
be used here also, but the visible advance of the projecting screwed stem 
informs the operator what he is doing. The stem has only straight 
motion through the stuffing-box without twist, and the threads are 
easily lubricated. The gate-valve should be placed with its spindle ver- 
tically upward or on its side: if the spindle, is downward, water gathers 
in the gate recess and gives trouble afterward when expelled. Fig. 
317 shows the types of small gate-valve with bronze body and screwed 
and flanged outlets, and " advancing and non-advancing stems." 
In large work and with high pressures the force pressing the gate upon 





Fig. 317. 



Fig. 318. 



PIPING OF PRESSURE TO ENGINE AND ACCESSORIES 353 

its seat on the side opposite the pressure before the pressure reaches 
that opposite section of the pipe is very considerable. It may be 
enough to make it very hard to move the valve to open it. It is further 
undesirable to open any large area from the high-pressure to the low- 
pressure side of the valve until the pipe has grown warm and the pro- 
visions for the drainage of the pipe have gotten rid of the condensation 
due to the heating process. This has resulted in the placing of a by- 
pass and. valve of comparatively small diameter to lead steam around 
the gate when the by-pass is open, while the main gate is still closed. 
Even carelessness cannot get steam too fast round into the cold pipe 
beyond the gate: and as pressure and temperature are established 
equally in both sides, the main gate can then be opened both with care 
and safety (Fig. 318). Partial opening of a large gate, and particularly 
of one with loose faces, is not desirable: it injures the face contacts and 
makes the joint leaky. Mechanical erosion and dirt in the flow through 
the valves are injurious to both faces, as well as rust. The contacts 
should not be of the same metal, to lessen the danger of their rusting 
together when closed for a considerable interval. Bronze and iron are 
the usual combination. 

A large gate-valve cannot be quickly closed with a screw-motion. 
The gate must be moved through more inches than the diameter of the 
opening or pipe, and the pitch of the spindle thread should not be too 
steep, lest power be sacrificed, or the valve be too hard to move. Com- 
binations have therefore been proposed where, on emergency for throttle- 
use, the thread and nut can be cut out, and the valve closed by straight 
push. This can also be made a safety stop (paragraf 494) by attach- 
ing a weight to the spindle and the emergency mechanism to the detent. 
When the detent is released the valve is shut quickly by the weight, 
while in normal use the gradual opening by the wheel and screw and nut 
is available. 

In very large valves the cross section becomes so great that two 
spindles will be advisable, working in unison by being geared together. 
Here the hand-wheel will be replaced by a ratchet and lever; but the 
hand motion will be exceedingly slow. This has given rise to the motor- 
driven valve, in which the hand-wheel of the smaller sizes becomes 
a large-diameter spur gear, which is driven by the small pinion on 
an electric motor armature shaft. This principle of valve-operation 
leads very simply to that of valve-control by switches for these valve- 
motors, the wires leading to the motors from the switches which are 
located at a point of centralized control. Valves can be instantly 
operated in case of emergency even if at considerable distances or 
elevations in the plant. 



354 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



There are also special valves in a modern plant having to do with 
requirements of varying pressures, functions and services, such as 
relief-valves, back-pressure valves, quick-closing valves and the like. 
Some of these will be referred to in connection with the exhaust- 
piping. 

243. Grading of Steam-pipe. Experience shows that when steam 
is moving in a pipe at high velocity it is impossible for water of con- 
densation to move against it. It will even be carried along upwards 
in a vertical pipe. Hence the steam-pipe should be graded downwards 
towards the engine from the boiler, and provision must be made near 
the engine to catch or dispose of this water. Trouble is often made in 
pipe systems using the ordinary fittings where horizontal branch outlets 
are made in the plane of the axis of the fitting, by reason of accumula- 
tions of water below the level of such outlets. Such pockets should 
either be carefully drained, or, better still, a special form of fitting 
should be used, such as shown in 
Fig. 320, in which the condensation 
will flow out of a main pipe with 
the steam which flows through the 
branch. A few pounds of water 
moving several hundred feet with 
a velocity of nearly a mile a minute, 
represents a mighty store of energy 
and is capable of most disastrous 
results. The presence of water in 
such pockets is also the occasion 
of mechanical erosion of the pipe 
similar to the action of the sand- 
blast, and ample provision must be made to get rid of even small 
accumulations. 

243. Drainage of Steam-pipe. Separators. To get rid of accumula- 
tions of water drawn mechanically or entrained by the steam from the 
boiler and those which result from condensation, at least five different 
methods may be used. 

The first is to tap into the pipe, wherever pockets and elbow-joints 
occur, small pipes with the necessary valves which can be left partly 
open and draw off water as fast as it gathers. These pipes may all 
converge towards a closed reservoir or tank from which the accumu- 
lated water may be pumped back into the boiler. These drip-pipes 
will vary in size with the quantity of water to be taken care of, but 
nothing is gained from having them too small, since they are likely 
to become clogged and inoperative. From one-half inch to one and 




Fig. 320. 



PIPING OF PRESSURE TO ENGINE AND ACCESSORIES 355 



f--iH 




one-quarter will be the usual range, according to the size of the pipe and 
engine in small sizes and two-inch or over in large ones. 

The second method is to diminish the losses of heat from the flowing 
of live steam through such tubes by the use of a steam-trap. A steam- 
trap is a pot within which is a device which is usually intended to act 
upon a valve or opening when water is to pass through it, but to refuse 
to act when water changes to steam. This result is secured in many 
ways in different designs of trap. The simplest plan is to have the 
trap inclose a float which is acted upon by water, and raised, but which 

falls in steam (Fig. 321). It will 
be seen that when the drip-pipe 
connected to the trap is filled with 
water, the float will lift and open 
the connection through which that 
water can escape. When trap and 
pipe are emptied of water the float 
will fall, closing the outlet from 
the trap, and shutting off escape 
until the trap is again filled. The 
discharge from these traps may 
either be back into a closed tank to 
be pumped into the boiler, or it 
may be wasted into drains (w^hich is 
not to be commended). Many traps instead of using a float are oper- 
ated by differences of expansion of one or two metals in steam and 
water, and there are many practical ways of applying the floatation 
principle. In Fig. 322, for example, are three ways of using the ball 
float. The upper left one makes. the float actuate a sliding-valve : the 
valves in the others lift off their seats, but the lower one subdivides 
the valve area so that the opening is progressive and graduated to 
the amount of water coming in, and the principle of the water-seal 
is used to keep solid water only in the outlet pipe until the outlet 
valves have been shut by the descent of the ball. The principle may 
also be used of the counterpoised pot, in which the empty vessel swings 
up on its trunnion or pipe near its center of gravity when empty; as 
it fills the end further from the trunnion grows heavy and overweighs 
the counterpoise, causing the pot to fall through an angle ample enougn 
to work the valve (Fig. 323). 

The third method is to introduce a receiver or catch-water tank in 
the pipe close to the engine into which all condensation shall be made 
to flow, and out from which only dry steam will go to the engine. 
Such a receiver may be a pipe (Fig. 324), or a simple vertical cyhnder 



Fig. 321. 



356 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

Inlet 




Fig. 323. 



I 



PIPING OF PRESSURE TO ENGINE AND ACCESSORIES 357 



K 



is 



m^ 



DRAIN COCK 
Fig. 324. 





Fig. 325. 



Fig. 326. 




358 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



of boiler-plate (Fig. 326), into the top of which the steam-pipe enters 
and passes down part way. The water which is carried by the steam 
falls to the bottom by its inertia or by gravity, and will there be taken 
care of either by a drip-pipe or by a trap. The steam going to the engine 
leaves the receiver from a point near the top, and the enlarged diameter 
which diminishes the hnear velocity of the steam prevents the out- 
flowing current from drawing out the entrapped water. A glass tube 
can be attached to the side of the receiver so that the level of the 
water caught in it can be easily observed and its discharge governed 
accordingjy (Fig. 326). 

The fourth method is easily derived from the foregoing. It is the 
use of a separator to withdraw by mechanical means water which 





Fig. 328. 



Fig. 32^. 



the steam has entrained. There are several forms of such separators. 
Several of the most successful ones are shown in Figs. 325, 327, 
328 and 329 and their methods of application are obvious. It will be 
seen that the principle involved is that of giving a spiral or centrifugal 
motion to the water and steam as they enter the separator. The supe- 
rior density or weight per cubic inch of the water causes it to yield 
most strongly to this centrifugal tendency, and it goes to the outside 
of this chamber, while the lighter steam, being less affected by this 
tendency, will remain nearer the center, from which the outlet to the 
engine is taken off. The presence of metallic-surface perforated 
deflecting or baffle-plates and similar constructions increases the 
efficacy of the separation since water divided in drops has a tendency 
to attach itself by capillary action to such surfaces. The separator 
requires to be, in the form shown, of a diameter at least twice that 
of the pipe, and the depth or length at least three or four times its 
diameter. The larger the separator, the more efficient, since it com- 



PIPING OF PRESSURE TO ENGINE AND ACCESSORIES 



359 



bines in this case the natural separation by differences of specific 
gravity with the mechanical separation by centrifugal action. The 
separator acts as a receiver when accidental quantities of water are 
thrown over with the steam. With reasonably dry steam (having five 
per cent of water in it or less) an effectual separator should allow 
less than one per cent of water to pass it and reach the engine. The 
discharge from the bottom of the separator may be taken care of by 
a trap, or it may be freed by hand as above described. Figs. 328, 



HORIZONTAL 




Fig. 330. 

329 show centrifugal separators for a horizontal and for a vertical line 
of pipe. The heavier water is thrown radially and caught in the 
receiver below (see also Fig. 333). 

A substitute for the trap, forming a fifth system, has been worked 
out for use in places to which it can be satisfactorily applied. It is 
called the steam-loop and is shown in Fig. 330. The pipe from the 
bottom of the separator becomes a species of siphon, w^hose length of 
leg is depended upon to move the water in it by the differences of 
density of the water in the two legs. In the drop-leg of the loop, which 
is connected to the boiler below the water-line, the water is compara- 
tively still and solid. In the other leg or riser the water is mixed 
with steam in bubbles ascending up through it, and this difference 
in weight will maintain a continual discharge into the nearly horizontal 
member which is slightly graded towards the boiler. The steam- 
pressure is nearly in equilibrium at the level of the water-line through 



360 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

the system, but the weight of sohd water in the drop-leg gives the 
dynamic head to feed the condensed water continuously from the 
dfop-leg into the boiler. 

339. Non-conducting Coverings for Steam Pipe. To meet the fifth 
requirement of paragraf 231 respecting loss of heat by radiation and 
contact of the air around the pipe, a material of low thermal conductivity 
must be used as a cover or jacket around the pipe. It must keep 
air-currents from the pipe and must resist by its properties the tendency 
of the pipe to radiate. These two requirements must be kept in view 
in selecting the material to be used. The material must furthermore 
be resistant to combustion and deterioration under heat, and must 
give off no disagreeable odors. It must be easily applied, must be 
cleanly and not attractive to vermin, and it is desirable that it be so 
made that repairs and alterations to the pipe may be made without 
destroying the non-conductive covering and making its renewal neces- 
sary. These latter conditions point to the use of what are called 
sectional coverings. It should also be as cheap and light in weight 
as is consistent with effectiveness. 

Since air undergoes no heating by radiation, but is heated by contact 
only, it has been found that materials of such porous or fibrous character 
as to shut in or occlude a considerable quantity of air, finely subdivided, 
make the best non-radiating coverings. The air is easily heated by 
contact, so that care must be taken to prevent this air from circulating, 
and it is best to keep it from actually touching the pipe. These 
peculiarities form the basis for the excellence of many combinations 
which US3 hair-felt. The porous or fibrous quality of the hair-felt holds 
a large quantity of air while circulation is precluded, and injury to the 
hair is prevented by first wrapping the pipe with asbestos-board. 
The hair is held in place by a canvas covering sewed over it, and if 
desirable bound by sheet brass or nickel-plated rings for appearance' 
sake. The fiber of asbestos or of blast-furnace cinders comminuted 
by blowing air or steam through it while fluid and known as mineral 
wool, possesses the same qualities as hair-felt, and for the same reasons. 
Other materials of successful use as non-conductors belong to the 
class of the earths. Infusorial earth largely composed of the silicious 
shells of minute diatoms, magnesian earth, ashes, and the like, made 
into a plaster with some binding material like asbestos-fiber or hair, 
form a group of non-conducting coverings often to be met with and 
which form the plastic class. The sectional coverings or removable 
coverings are combinations of asbestos-paper, hair, and canvas molded 
into split cylinders which are sprung on over the pipe, closed together, 
and held by decorative bands. It is apparent that to increase the 



f 



PIPING OF PRESSURE TO ENGINE AND ACCESSORIES 



361 



thickness of the coverings in order to diminish loss of heat through 
them is to increase the cost of such coverings and the weight on the 
pipe. The presence of the covering compels the hanging appliances 
to adjust themselves for expansion without disturbing the covering. 

The standard method of testing the conductivity for heat of such 
proposed coverings has been to take a given length of the bare pipe in 
an open basement or space of still air of observed temperature, and 
admit st^am of known observed quality as to moisture temperature 
and pressure at one end and to observe the weight of water condensed 
and drawn from the other end in a given time. The heat loss in units 
from the latent and sensible heat of that weight of water is then 
computed and called one hundred. The pipe is then covered in 
succession with the coverings to be tested, and the same measurements 
and computations are made. The covering giving the least heat loss 
in units is then put at the top of the list as having the greatest 
negative conductivity. There can plainly be no absolute standard. 
Other methods have been to replace the steam heat by the heat in an 
electric resistance coil, and observe the heat transfers through one 
square foot or unit area to absorbent water outside of the covering, 
and eliminate the variable effect of air currents in a pipe test. 

Some experiments of the late Chas. E. Emery have always appeared 
to have some special practical value and are given in Table XIII. 
They refer to hair-felt as a standard, used in a layer of two inches thick. 

TABLE XIII. 



HELATIVE EFFECTIVENESS OF 2-INCH LAYERS IN PREVENTING LOSS OF HEAT. 

(Emery.) 



Material. 


Effectiveness. 


Material. 


Effectiveness. 


Hair-felt 

Mineral wool 


1000 
.832 
.715 
.680 
.676 
.632 
.553 


Loam (peat moss fiber). . . 
Slaked lime 


0.550 
.480 


Mineral wool and tar 

Sawdust 


Gas-house charcoal 

Wood charcoal . . . 


.470 
630 


Mineral wool (inferior). . . . 
Charcoal 


Asbestos alone 


363 


Coal ashes 


345 


Pine wood (cross-grain) . . . 


Coke alone 


.277 


Airspace (circulation un- 
checked) 


.136 



Similar researches have also been made by Ordway, Barrus and Brill' 

* Consult 

Emery, Transactions A. S. M. E., vol. ii. p. 34. 

Hutton, Transactions A. S. M. E., vol. in. p. 228. 

Ordway, Transactions A. S. M. E., vol. v. pp. 73 and 212. 

Ordway, Transactions A. S. M. E., vol. vi. p. 168. 

Brill, Transactions A. S. M. E., vol. xvi. p. 827. 
-See also Kent's Mechanical Engineer's Pocket Book. 



362 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



245. Exhaust-pipe. The computations of paragraf 231 apply also 
to the design of an exhaust-pipe, except that the pressures will be lower, 
and it is not desirable to demand from the engine-cylinder that it should 
exert as back-pressure upon the working piston the force necessary to 
accelerate the used steam out of the cylinder and to the atmosphere or 
to the condenser. Such pressure upon the 
exhaust-steam is a subtraction from the for- 
ward pressure upon the other side of the 
piston which is doing the work of that stroke. 
Hence the practice is usual to make the 
velocity in the exhaust-pipe two-thirds of 
that permitted in the high-pressure steam- 
pipe, and compute 4000 linear feet per 
minute as the permitted velocities. Bends 
should be with long sweep and as few in 
number as possible. 

In the general or ideal case, where exhaust- 
steam is not to be used for heating, the pres- 
sure in the exhaust-pipe will be that of the 
atmosphere, or at most a pressure ranging 
from that up to three pounds per square 
inch. Hence it need not be of the same 
strength as the steam-pipe, which explains 
the use of spiral-riveted or spiral-welded 
pipe in long lengths (Fig. 331). Lightness 
and cheapness are thus secured. In city 
conditions the exhaust-steam must be taken 
to the roof of buildings or factories to be 
discharged, which compels a considerable 
ascending length of pipe. In power-plants 
where this does not have to be considered 
the engine may exhaust into the open air 
at its own level. Where the noise of the 
exhaust is of no consequence as it escapes 
into the air, the end of the pipe may be 
bare. Where noise must be prevented, and 
where the cUscharge of condensed water in 

the exhaust-current carrying oil from the cylinder is objectionable or 
harmful to roofs or structures, provision must be made to meet both 
of these difficulties. The exhaust-pipe must be carefully drained to 
remove the trouble from pulsations and noise from such water in 
pockets where the motion of the steam can impel the water in ir.asses 




Fig. 331. 



PIPING OF PRESSURE TO ENGINE AND ACCESSORIES 



363 



against bends, and yet be unable to expel it. The oil from the 
lubrication of the cylinder is also objectionable in condensing-engines, 
where the condenser first gets it and later it enters the boiler with the 
hot-feed from the hot-well. The exhaust-pipes will therefore have oil- 
separators and an exhaust-head. 

246. Oil-separators. The oil injected into the cyHnder with the 
steam by any system to lubricate the pistons, valves and rings (para- 
graf 528) will most of it be carried out with the exhaust. There only 




Fig. 332. 



remains behind what adheres in a thin film to the metallic surfaces. 
With high pressures and superheated steam the oil may be made into a 
vapor or a mist in such fine division that it will not form again into 
drops on lowering of temperature. In general, however, the oil retains 
its character and structure and its property of adhering to metal sur- 
faces against which it impinges. The first principle of oil-separation is 
therefore to baffle and buffet the current of outgoing steam and make 
it easy for such oil as is in drop form to reach an adherent surface where 
it can be caught. 

The action seems to be a capillary one, the oil adhering but the steam 
passing on. Figs. 332, 333, 334, and 335 show the baffle-corrugated 
systems, and Fig. 338 the inertia principle. Here the steam passes over 
trough-shaped projections as it is deflected, and in these troughs is 
enough water at all times to entrap the oil and hold it till it overflows. 

The wetter and cooler the steam the more effective are separators of 
these types. With hot and high-pressure steam the oil is in so fine a 



364 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

state of division that it does not become entangled at the high tem- 
perature of the baffling-surfaces, and here a species of filtration seems 
the only practical way. 

The filtration scheme means a leading of the exhaust through a box or 




Fig. 333. 




Fig. 334. 



Fig. 335. 



enlargement of the pipe in which shall be installed some material with 
a large contact surface and open porous structure. Hay or straw has 
been much used in marine practice and with condensing-engines for the 
filtering material: compressed sponge or even sand. These must of 



PIPING OF PRESSURE TO ENGINE AND ACCESSORIES 



365 



course be frequently renewed and it is a dirty and offensive job to clean 
the filter. The design of Fig. 336 is the Edmiston cheese-cloth filter 
which has been much used by reason of its convenience. The disks 
1, 2, 3, 4 are frames which can be inserted through the hinged lid, and 
are "held in place b}^ the spider set up from outside by the screw a. 




Fig. 336. 



Soda can be introduced by the cup to make a soap of viscous oil for 
cleansing at intervals. The steam can be by-passed if renewal of the 
filter-cloth is desired without stopping the engine. 

The oil which has been through the cylinder is usually so lowered in 
lubricating quality by the heat and abrasive contact that it is not worth 
while to try to save it and use it again except for the roughest and most 
unexacting service; it is usually run to waste. If saving is worth while, 
the oil is filtered again in special oil-filters to remove dirt which has been 
gathered from pipes and elsewhere, and quite often some unused oil is 
added to it to bring up its quality. But the heat and use has produced 
an oxidation of the oil-elements and brought it nearer the state of gum 



366 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

in which it is useless, and hence with hot steam the inexpediency of the 
trouble and expense of its redemption. 

In the condensing engine, the oil from the exhaust-steam which the 
separator does not entrap goes forward to the vacuum chamber or 
condenser which is kept cool by the cooling injection water by which 
condensation of the exhaust is effected making hot water of it. Some 
oil therefore gathers upon tubes or other condensing surfaces and by 
forming a coat or crust interferes with the effective action of such 
surfaces, or clogs the passages when these are small tubes. The con- 
denser must therefore be cleaned at intervals long or short according as 
the separator is effective or not. What is not stopped in the condenser 
goes forward to the hot-well from which the feed-pump takes its suction 
and pumps water into the boiler. The oil floats on the surface of the 
water of such hot-well, and if the suction can be always taken from the 
bottom of the well, this works as a further separator. What oil is 
churned up in the hot-well and does not separate here by Kquation, 
is sent forward into the boiler where it probably remains except so far 
as blowing-off removes it (paragrafs 50 and 187). What remains, 
adhering to the metal of heating-surfaces, keeps the water from intimate 
contact with the steel and causes overheating (paragraf 192). 

247. Exhaust-heads. In the non-condensing engine where exhaust 
goes to the atmosphere, the oil may be expelled from the end of the pipe 
in cases where its fall to the ground or overboard is not objectionable. 




Fig. 337. 



In cities, however, and when the exhaust-pipe goes vertically through or 
above a roof, such rejected oil is a menace and an annoyance. It is a 
nuisance from the defilement of it; a fire menace where it accumulates; 
a detriment to the roof covering. In cities 



moreover, the noise of 



PIPING OF PRESSURE TO ENGINE AND ACCESSORIES 367 




Fig. 338. 



pulsating exhausts is an objection. Hence the design of devices for the 
end or outlet of the exhaust-pipe which shall have an enlargement of 
volume sufficient to break up pulsations and substitute for them a 
continuous flow at reduced pressure, and which shall also here entrap 
the oil at the time of such reduction of velocity. 
The exhaust-head as a muffler or silencer will 
have a section of a cone with its large base 
upward. The exhaust will rise into this enlarged 
area inside and will there be deflected either by 
the orifice of the pipe or by baffles, so that 
expansion, reduction of pressure, cooling, and 
inertia opposition shall all be secured. What 
escapes from the center of the conical head will 
therefore be water above 212° rather than 
steam-gas, and wifl flow softly away: the water 
below 212° and the oil wifl be gathered from the 
sides and from the baffles and will be led down to 
disposal at the ground or into drainage. Figs. 
337 and 338 will suggest types of such exhaust- 
heads. There is a great variety of designs in use. 

Chemical means for coagulating and eliminat- 
ing oil from tanks and receivers using alum most often are open to the 
objection that they need continual care and skilled superintendence to 
secure efficient working. 

248. Back-pressure Valves. The exhaust-steam from a non-con- 
densing engine carries heat units enough to do a considerable share of 
the heating of buildings in mild winter weather if led into the heating 
radiators of a steam-heating system. Such steam may also heat hot 
water for circulation and heating when the steam would be incon- 
veniently hot. In any case where heat is required for industrial or 
other uses, and steam would have to be made directty in boilers for the 
purpose if the exhaust were not so used, it is a measure of administrative 
economy to utiHze the exhaust in this way. The net economic result 
may be that the plant gets its power for nothing in the way of fuel 
expense, the engine operating as a pressure-reducing valve between the 
boiler and the heating-coils or tanks (paragraf 244). In such sj^stems 
and under other circumstances it is desirable that there should never 
be an excess of pressure in the utilizing coils or elements due to any 
increased use of steam in the engine and increased volume rejected, or 
by reason of any shut-off of the heating-coils. This will be met by 
what are called " back-pressure " valves, which are loaded check- valves 
in effect, opening in one direction and not in the other, and held shut by 



368 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

a known and adjustable pressure. When the set pressure is exceeded, 
the back-pressure valve automatically opens and acts as a rehef of 
excess pressure as long as it lasts. When the pipe and valve are large, 
it becomes of advantage to use differential plans, and to use such systems 
of loading the valve for control as shall increase the opening as the 
differences of pressure increase. Fig. 339 shows the spring-loaded 
check-type at the right and the differential or partly balanced poppet 
type on the left. The weighted lever in the latter need provide only 
for such pressure as will supply the desired difference between the 
higher pressure at the right-hand inlet below the large seat and the 





Fig. 339. 



lower pressure above the upper and below the lower, and keep the valve 
down in place until the pressure at the right gets too high. Back- 
pressure valves of these types will be used also where a vacuum might 
be caused in an engine exhaust connected to an open heater at any time, 
resulting in a danger of back flow of feed-water into the engine and 
consequent danger to its cylinder: or where two systems of different 
pressures are cross-connected and the undesired higher pressure might 
establish itself in the lower system without such relief. 

249. Reducing Valves. In severe weather in the northern climates, 
the exhaust -steam may not furnish heat enough for the heating-coils, 
and it becomes desirable to bleed from the high-pressure main pipe into 
the low-pressure heating-pipe. Or in storage systems of compressed 
air or other energy, it may be desirable to put the storage tanks under 
very high pressure and allow only a fraction of such great pressure to 
reach the motor. There are many other cases where the pressure on 
the lower side of the valve should be proportionately lower than on the 



4 



PIPING OF PRESSURE TO ENGINE AND ACCESSORIES 



369 



high, either in a ratio or in an amount, and that this should be fixed so 
that no carelessness or ignorant handling of valves should release the 
high pressure. Such regulating- valves are called reducing-valves and 
any back-pressure valve with controllable load becomes a reducing- 
valve in principle if adjusted for the desired difference of pressure. 
When the reduction requires to be to a determined lower intensity and 
not to a ratio between the higher and lower pressures, the valve must 
have the passage for the flow of steam varied by the intensity of that 
reduced pressure, and such designs as Fig. 340 result. The low pressure 
and the weighted lever act together to operate the valve in opposite 




Outlet 



Connect with Low Pressure Side 




Fig. 340. 



senses at the left hand, and the balance between the two determines the 
amount of opening. I^ the right-hand cut the balance is between the 
spring and the low pressure over the area of the plunger. 

250. Drip Connections. In addition to the considerable piping 
required for the drainage of the main pipe line discussed in paragraf 
238, there will be also pipe connections to the engine itself and its 
attachments, jackets, reheaters and the hke for the removal of water 
and condensation. These are not usually continuous in their operation, 
but will only be used in starting or to relieve excessive accumulations, 
and may or may not be fitted with traps. Neither do separators attach 
to them as they carry solid water only. Their discharge is either 
wasted, or led to the hot-well or condenser of condensing-engines or into 
a receiver tank from which pump suctions draw. They will be there- 
fore referred to again under the engine treatment. 

251. Concluding Comment. The piping of auxiliaries offers no 
problems not covered in the general foregoing treatment. There are 



370 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

often special features such as the by-pass in compound engines through 
which boiler-steam can be led past the first cylinder to a later in series, 
in case the piston in the former should be upon the dead-center of its 
mechanism or its valve-function; the spindle or stem of valves may 
be lengthened to bring the wheel at convenient heights above the 
flow, and special casings may be used to inclose such spindles for 
appearance and for steadiness in large engine installations. There will 
also be water-piping for supply of water to auxiliaries, but these will 
not be under high pressures and the usual standards of low-pressure 
work will apply. 

Where steam-pipe lines are led in duplicate from the boilers to the 
engines to minimize the danger of shut-downs the duplicate lines must 
come together at the boiler outlet and at the engine inlet. There will 
be valves close to both boiler and engine so that both lines may be 
cut off in case of repair to either boiler or engine. Any failure in the 
last link and between boiler and first valve or between engine and last 
valve is credited to boiler or engine and puts it out of commission. 

In this chapter the energy derived from combustion and heat has 
been transmitted in the form of pressure to the throttle-valve at the 
engine, by which its delivery to the latter is controlled or arrested. 
The next step forming the next part of the treatment is the machine 
receiving this pressure-energy and transforming it from pressure in 
static form into work, or energy in dynamic form, of force moving under 
control through a space. Such a machine is called an engine. 



PART V. 



CHAPTER XV. 

THE ENGINE. 

254. Introductory. The pressure in the steam-pipe is a static force 
or only a potential energy until such force measured in pounds per unit 
of . area pressed is made to overcome a resistance moved through a 
space in feet. So long as the throttle- valve in the pipe from the boiler 
is closed and tight, the heat energy of the burning fuel is either being 
stored in the water or being wasted. What is needed is some device 
to receive this pressure, to move under that pressure so that a product 
of feet into pounds shall give a number of units of work. 

This pressure can be tmnsformed into work in two ways. The 
pressure can be exerted over an area so confined in a vessel or chamber 
that motion of that area is possible only in one direction. This area 
is called a piston. Its confinement is in a cylindrical chamber which 
is called the cylinder. The energy or work of one traverse of the 
piston is PA (Fig. 4, paragrafs 3 and 6) . The other way is to let the 
steam escape through an orifice or jet into a more open chamber where 
the pressure is lower. The weight of steam passing the orifice of the 
jet has a mass M and a velocity in feet per second v. The product 
Mv is equivalent to a work in foot-pounds per second, and if such 
mass impinges upon a surface capable of absorbing such impulse 
completely, the second type of engine results. The first is a pressure- 
motor; the second. is an impulse-motor. No other ways are known for 
making the steam-pressure energy do mechanical work. The one 
system gives piston engines; the other system the turbines. 

The only continuous motion is the motion of rotation, like a wheel 
around its axis. Straight-line motion cannot be continuous in the 
same direction; the best which can be done is to make the direction 
alternate first in one direction and then in the other. Such alternating 
straight-fine motion is called reciprocating. The turbine motors 
acting by impulse of the steam mass at high velocity can be continuous 
in rotative effect if the blades or organs receiving the impulse can be 

371 



372 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

made to revolve. This is easy to do. Pressure motors can also be 
made rotary if the piston receiving pressure and fitting its surrounding 
casing can be made steam tight and the motion of the piston around 
an axis be transferred to the shaft in the axis of rotation. The pistons 
are blades upon the arms of a wheel fast to the shaft. Ordinarily, 
however, the piston is made to reciprocate in a straight line in a 
straight cylinder: and some mechanism of practical sort is necessary 
to transform this intermittent reciprocating motion of the piston into 
a continuous rotary motion or revolution of the engine-shaft from 
which the power is taken off. 

There would appear therefore to be three classes of engine possible: 

1. The velocity or impulse type, continuous rotary; represented by 
the steam-turbines. 

2. The pressure type, continuous rotary; represented in all rotary 
piston engines. 

3. The pressure type, intermittent reciprocating transformed by 
mechanism to continuous rotary motion at the shaft only; represented 
by all straight-cylinder and connecting-rod crank engines. These will 
be called reciprocating engines. 

The turbines and the rotary steam-engines would appear to have every 
antecedent advantage in their favor. There must be some considera- 
tions from the behavior of steam in the cylinder or from a mechanical 
point of view which have given to the reciprocating engine its vogue 
and acceptance in competition with the others. 

Historically the first steam-engines of practical sort were for pumping 
water. In the Savery form the steam-pressure was exerted directly on 
the surface of water in a chamber to force it out and upward, although 
the piston had been proposed by Denis Papin in 1680 to keep the hot 
and cold masses apart. The Newcomen and Leupold designs used the 
separate pump driven through a lever or beam, and as the pump was a 
reciprocating element in a pump-barrel, the engine was made on the 
same lines. Watt followed Newcomen; and subsequent development 
hesitated to abandon the excellences of the reciprocating type. These 
excellences are twofold: the mechanical perfectness of the crank 
for its purpose; the thermal advantages of expansive pressure working 
in a cylinder of definite volume and low clearances. Hence the recip- 
rocating type of piston motor will be first treated as the form pictured 
to the mind when the word '' steam-engine " is used, leaving the 
simpler rotary engine and the steam-turbine for later discussion. 

255. The Ordinary Steam-engine. When the word '' steam-engine " 
is used without qualifying terms, and in advance of special study of 



THE ENGINE 



373 




374 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

form and arrangement it brings before the mind a machine such as 
Figs. 345 and 346. Here at the left hand is: 

1. The cyUnder. This has (2) a " cover " fastened on with studs 
and nuts or with tap screws, and is surrounded with a hollow space or 
(3) *' jacket " in which is either a non-conducting material (para- 
graf 239) or else it is an air-space, or a steam-jacket. In this cylinder, 
is (4) the piston. This fits the bore of the cylinder reasonably close, 
but not so perfectly as to run any risk of its being seized by the walls 
of the cylinder in case the piston expands by heat and the walls do not. 
To make it tight so as not to let pressure leak past its faces of contact, 
the piston has (5) '' piston-packing rings " which are flexible and yield 
radially but prevent leakage from one side to the other. The piston 
must not be in any danger of hitting either cylinder-head, and hence 
there is a fraction of an inch of (6) '^ clearance " at each end. 




Fig. 346. 



The cylinder being of limited length, the piston must move back and 
forth in it first in one direction and then in the other. Steam-pressure 
from the pipe and boiler should be admitted to the cylinder and piston 
alternately, first on one end and then upon the other. If so, the engine 
is double-acting. If steam-pressure comes only on one face of the piston 
— always the end away from the crank or towards the head of the 
cylinder, and hence called the '' head-end" — the engine is single-acting. 
The end of the cylinder which is toward the crank and shaft will be 
called the " crank-end." The steam which has driven the piston on 
one stroke must be expelled or " exhausted " upon the return of the 
piston on the next stroke. This function requires openings into the 
cyUnder called " ports " and a " valve " (Fig. 346) and its valve-gear 
to operate it in phase with the piston-stroke. The area of this piston 



[-f]> 



in square inches and the pressure P on each square inch 



give when multiphed together the quantity PA of paragraf 3; and the 
length of the traverse in feet L multiplied by PA, or PAL, is the foot- 



THE ENGINE 375 

pounds of work done in each complete stroke (paragraf 6). The 
length of the cylinder inside will be the sum of the stroke, the piston ■ 
depth and twice the clearance allowance. 

The energy represented by PA is developed inside the steam-tight 
cylinder. It must be made available outside, and the motion of the 
piston suitably controlled. Hence there will be rigidly fastened to the 
piston 

(7) The piston-rod. This is pushed out of the cylinder and pulled' 
in alternately. It comes into the atmospheric pressure outside the 
cylinder through a construction called the (8) '' stuffing-box," allowing 
the rod to slide through the inside cover or crank-end of the piston 
without leakage or loss of pressure, and yet with a minimum of needless 
friction. The area of the crank or rod-face of the piston is less than the 
head-face by the area of the cross-section of the rod. Hence the inner 
stroke is less powerful than the outgoing one by this difference in the 
value of A when P is the same on both sides. 

The piston-rod though stiff is not inflexible: and it is apparent from 
the illustrations that at the moment chosen there is a considerable side- 
thrust on the right-hand end of the rod. Hence to guide this free end' 
of the piston-rod will be required 

(9) The cross-head. This is compelled to move in a line parallel 
with the axis of the cylinder by (10) guides. The cross-head and guides 
prevent the piston-rod from flexure (if the guides do not yield themselves) 
and keep the stuffing-box from wearing out of round and leaking. In 
the design shown in Fig. 345 an extra partition-plate is introduced on 
account of the method of oihng chosen, but ordinarily the guides come 
close to the crank-end of the cylinder. Connecting the (11) " cross-head 
pin " to the crank-pin at its other end is 

(12) The connecting-rod. This is a requirement of the mechanism to 
convert the reciprocating motion common to the piston, its piston-rod 
and cross-head, into the rotary motion desired for the shaft. It will 
have provision to take up wear on the pins at each end, (13) " brasses," 
and will be twice the length of the crank on the shaft or over. 
Its presence is necessary but it is of no dynamic advantage. The 
connecting-rod transfers the alternate push and pull of the piston-rod 
to (14) the crank-pin on the (15) crank of the (16) crank-shaft. The 
crank-pin has to receive the entire force PA (less the modification due 
to any angularity of the push of the connecting-rod) and turn the crank 
against the resistance upon the crank-shaft, and must do this by a 
rubbing contact of the brasses upon the cyhndrical pin. The 
leverage of the crank to revolve the shaft may be called its '' torque " 
or turning-moment. In the form shown the crank is counter- 



376 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

weighted opposite the pin to balance the inertia effects of the massive 
connecting-rod. 

Beyond the (17) '' main bearing " of the crank-shaft just behind 
the crank is (18) the fly-wheel, acting as a regulating device for uniform 
rotation, and whatever may be the form of the application of the 
resistance, either by a belt-wheel or gears or generating dynamo. In 
locomotives and marine practice there is no fly-wheel as the driving- 
or water-wheels supply this regulating influence as well as the mass 
propelled. 

The typical skeleton mechanism is therefore: 
1. The cylinder. 
4. The piston. 
7. The piston-rod. 
9. The cross-head. 

10. The guides. 

12. The connecting-rod. 

14-15. The crank. 

The crank is the controlling element, as well as the power trans- 
mitter. Hence the radius of the crank determines or fixes the unit 
for all else. Because the length of 

1. The stroke L is exactly two cranks. 

2. The cylinder is two cranks and allowances. 

3. The piston-rod is two cranks and allowances. 

4. The guides are two cranks and allowances. 

5. The connecting-rod is 2-2^-3 cranks. 

From the head end of the cylinder to the tip of connecting-rod 
when at its furthest point is therefore a total of seven cranks and 
necessary allowances. 

It will be serviceable to examine the kinematic principles underlying 
this mechanism. 

356. The Kinematics of the Crank-connecting-rod Mechanism. 
Some Engine Mechanisms. The combination of the crank-arm, the 
connecting-rod, the constraint of the cross-head in its guides and the 
bed-plate which keeps the center of the crank-shaft in a fixed relation 
to the path of the cross-head, shows that kinematically the typical 
steam-engine is a four-bar or four-link mechanism (Fig. 347). Of 
this the crank is No. 1, the connecting-rod is No. 2; an arm with a 
center at an infinite distance at right angles to the guides is No. 3, 
and compels it to a translation in a straight line at right angles to such 
swinging Hnk of infinite length. The bed-plate fixing the center of the 
first link and the path of the cross-head, is in effect the fourth link, 
joining the center of the crank-shaft with the center of No. 3 at an 



! 



THE ENGINE 



377 



infinite distance (Fig. 348). If now the fixed link in the chain be 
made No. 2 of the series, then keeping No. 1 still the crank-arm, No. 3 
and No. 4 must adjust themselves to the rotation of No. 1 around 





Fig. 347. 



Fig. 348. 



its other end, and the chain appears as in Fig. 349 with the power 
appHed to turn the crank along No. 4. The link No. 3 must therefore 
swing around the other fixed end of No. 2 and an engine with oscillating 




Fig. 349. 



cylinder results. If instead of making No. 3 of considerable length 
it has the radius of the trunnion of the oscillating cylinder, the engine 




Fig. 350. 



appears in its more recognizable form of Fig. 350, and the piston 
functions as connecting-rod also. 

If now the piston-rod-element be eliminated from the type-design 



378 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



to secure lightness in the moving mass for high speed, and shorten 
the length of the mechanism and yet avoid the oscillation of the cylinder 
masS; the kinematic chain remains the same, but 
the swing of the connecting-rod or link No. 2 must 
be allowed to take place within the cylinder in part. 
Fig. 351 shows this type in the shape much used in 
motor vehicles where the piston is made long enough 
to prevent cocking or jamming from the oblique 
thrust or reaction of the connecting-rod, and where 
the piston is of small diameter. When a large turn- 
ing moment is desired as where pressures are low 
the trunk engine takes the form of Fig. 355A in the 
Appendix, designed for a screw-driven monitor type 
to trim the weight in the hull and keep all of the 
engine below the water-line. (See also Figs. 403-5.) 
Finally to keep the engine short and yet have a 
long connecting-rod, the link No. 2 can be actuated 
from a cross-head behind the cylinder-head instead 
of having the cross-head between cylinder and crank. 
The connecting-rods for linking such cross-head to 
the crank-link No. 1 will be doubled for symmetry 
and pass outside of the cylinder on each side of it. 
Such an engine becomes a '^ back-acting engine." 
The types of mechanism are, therefore, 

1. The normal, or direct-acting engine. 

2. The oscillating engine. 

3. The trunk engine. 

4. The back-acting engine. 

Figs. 345 and 346 will stand for the normal direct-acting horizontal 
engine. Figs. 352 and 353 show the simplicity and directness of the 
oscillating or No. 2 type in small sizes; and the particular design is 
selected because the trunnion on which the cylinder oscillates as in the 
skeleton of Figs. 349-350 is made of a full size to reproduce the link 3 
in that diagram. Such engine will work equally well bolted to the 
ceiling, or as it were, upside down. It is more usually constructed in 
the larger sizes to meet the condition of Fig. 354, which is taken from 
European practice in side-wheel or paddle-boat engines. Here the 
overhead shaft carries the wheels. Steam enters at the left hand 
through the hollow trunnion and passes successively through three 
cylinders in series, escaping at the right. The short distance from outer 
cylinder-head to crank-shaft center enables such an engine to be gotten 
into shallow hulls for light-draft conditions. Oscillating engines were 




Fig. 351. 



THE ENGINE 



379 



much used in warships before the high-speed screw design came into 
vogue. The friction on the trunnions resulting in wear, resulting in 
leakage, and the slow rotative speed compelled when the cylinder 




Fig. 352. 





Fig. 353. 



masses are large has made the large oscillating engine of historic interest 
only. 

The third type or trunk-engine of Fig. 351 has been developed from 



380 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




THE ENGINE 



381 



that simple form intended to be single-acting into more complete forms 
where it has been sought to make it double-acting. In Fig. 355A, for 
example, in the Appendix is the true trunk-engine, double-acting. The 
piston area is the annular space surrounding the trunk which sUdes in 
and out through stuffing-boxes as though it were a hollow piston-rod. 
The internal diameter of the hollow trunk must be sufficient to let the 
connecting-rod clear the upper and lower elements when in the position 
of maximum departure from the axis nearly as shown. 

Such engines have an inconvenient diameter for the piston and a 
comparatively short stroke. The trunk at the back or head end is not 




Fig. 356. 

called for and is only put to equalize the values of PA on the outer and 
inner faces. If the rear trunk is left off, the engine is a half trunk such 
as illustrated at the right hand of Fig. 356. The left hand is the usual 
single trunk. In Fig. 357A in the Appendix is again a derivative type 
where mechanical effectiveness was sought by an extra long connecting 
rod, and the designer used the wasted area in the rear trunk to secure 
such length. It is applicable only to very short crank types and of 
small size. 

In Fig. 358 A in the Appendix is also a transition form where a half 
trunk of rectangular or long oval section was used to reduce inequality 
of effort up and down. This is much more troublesome to keep steam 



382 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 









Fig. 361. 



THE ENGINE 383 

tight and will not be used where it can be avoided. The normal trunk 
types are those of Figs. 351 and 356. 

The back-acting type of mechanism is an outgrowth of special con- 
ditions where the slow speed makes the mass of metal in the mechanism 
of secondary consequence. Fig. 359A in the Appendix is a type of such 
an engine derived from the earliest river-boat mechanisms, where the 
location of the crank-shaft above the keelson is at a determinate height, 
with no room for the cylinder below the shaft and a vertical cylinder is 
preferred. Two connecting-rods come down from the cross-head one 
on each side. The crank-shaft may or may not be continuous across 
the hull under the cyhnder. Fig. 360A shows the horizontal type for 
warship conditions, and where, as in Fig. 355, it is desirable to trim the 
ship by putting weights symmetrical with the keelson and below pro- 
tective water-levels. The piston-rod is made double and the two rods 
straddle the shaft in the first and fourth quadrant of the piston; 
the short connecting-rod bends back from the cross-head to reach the 
crank of the propeller-shaft. On the left hand are the condenser and 
pumps to balance the mass of cyhnder and piston. 

The back-acting design occurs most frequently in pumping-engines 
or blowing-engines for air. Fig. 361 is such a blowing-engine for low 
pressures and great volumes of air for blast-furnace practice. The 
steam-cylinder is just above the fly-wheel shaft, and from the cross-head 
at the top of the cylinder two back-acting connecting-rods descend 
outside the twin fly-wheels on each side to pins upon the large hubs of 
the wheels. The piston-rod is prolonged beyond the cross-head to 
receive and operate the blowing cylinder-piston above the platform. If 
the power were taken from the fly-wheel, this would be a true back- 
acting engine like Fig. 359. The fly-wheel function, however, is only 
of control and regulation, but it is desired fo have its bearings low down 
and near the ground. Hence the back action. This engine shows some 
details of piston construction and the use of poppet valves to be further 
referred to later. In Fig. 362 the same set of conditions is repeated in 
horizontal form for an air compressor of compact arrangement. The 
steam or power-cylinder is between the fly-wheels, and the crank-shaft 
behind it. The two connecting-rods and two cranks make it a back- 
acting engine at its power end. The air-compressing end on the pro- 
longation of the engine-piston is entirely free of the steam-engine 
mechanism, as in Fig. 361. In both cases, the cross -head should not be 
so rigidly fitted or keyed to the piston-rod as to be strained unduly if 
one of the rods wore more than the other at its bearings, so that they 
became of unequal length from center to center of bearing-pins 

It may be said in general, however, that these more complex mechan- 



384 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




CO 

6 

P4 



^l'HH'li»'l"i|iP;i;ili;' 



THE ENGINE 



385 



isms are becoming of less and less consequence as the advantages oi 
standard proportions become better realized, and the advantage of 
reducing the mass of material to be started, accelerated and stopped in 
each traverse of the piston. 

257, Deductions from the Kinematic Cliain of the Steam-engine. 

The recognition that the typical steam-engine mechanism was a four-bar kinematic 
chain with one link fixed has led to some serviceable deductions. 

First as to the relative velocity at any point of their unequal travel, of the crank- 
pin and the piston, or of the cross-head invariably connected to the latter. In 





Fig. 365. 



Fig. 366. 



Fig. 365 let O be the center of the shaft, OP the crank, PC the connecting-rod, and C 
the cross-head pin. The fixed link in the chain is No. 4 as in Fig. 348. If the 
number of revolutions of the engine is known, and OP is known or measured, then 
the velocity of the crank supposedly uniform is a x OP = viiais the angular velocity 
of the revolving crank = 2 nn. The velocity of the point C is then capable of being 
found or measured by the principle of the instantaneous or virtual center, which 
gives the link 2 or PC the same motion as it actually has by the concept of its being 
revolved around a center located by prolonging lines through the centers of its 
actual motion until these intersect. In this case, the motion of C is a rotation 
around a center infinitely distant above or below the line OC and perpendicular to 
the latter. The motion of P is as it were around the center X found by prolonging 
OP till it intersects the vertical through C. Then by the principles of rotation, 

Velocity of C X PX = velocity of P X CX 



Velocity of C: velocity of P :: CX: PX. 

If now from a line be drawn parallel to PC, and from P a perpendicular Pa be 
drawn to the latter parallel to CX, then the two triangles PCX and POa will be 
similar ; whence 

Velocity of cross-head: velocity of pin :: CX: PX :: Pa : OP. 

If the velocity be called constant and be represented to scale by the crank-radius 
OP, then the quantity Pa to the same scale represents the cross-head and piston 
velocity. An identical construction results when the center line of PC is pro- 
longed and a perpendicular OP is drawn to it, making P60 similar to PCX. 

If with the measured Pa or Ob for different positions of P as ordinates a curve 
be drawn with the diameter of the crank-circle = 2 OP as base, and a curve be 



386 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

drawn through the ends of these ordinates, the curve will represent the velocity 
of the cross-head for each position of P when the radius of the crank-circle repre- 
sents the velocity of the pin. It will resemble the dotted curve in Fig. 365 super- 
posed upon the crank-pin path. If the connecting-rod were of infinite length, or 
some mechanism were used which would keep the link 2 or the connecting-rod 
PC always parallel to itself and the line OC, then the velocity diagram of the cross- 
head becomes a circle, the ordinate in every case being the sine of the crank-angle from 
a zero in the line OC. (Fig. 366.) The yoke mechanism of Fig. 233 is a device to 
this end. 

This same conception enables the velocity to be computed with which the con- 
necting-rod brasses are rubbing upon the pin at any point of the crank-travel. The 
two elements at P may be regarded as being the contact of two gears, the radius of 
one being OP and of the other PX, or the radius to the virtual or instantaneous 
center. Let the angular velocity of the crank be a as before, and the crank-radius 
Re. These are known, and hence the tangential velocity common to the two ele- 
ments, which must be the same for the virtual rotation with an angular velocity h 
and a radius Rb. Then 

Rca = Rbh and b = -^~ = -^^ . 
Rb Rb 

When the crank and connecting-rod are revolving in opposite directions, the 
rubbing velocity will be the sum of the crank and connecting-rod rotations. If 
the crank-pin radius is rp, then the rubbing velocity will be 

Vr = rp{a+ b) 



= Tpa 



(^ - I) 



This is at its maximum when ^ is its maximum or when Rb is a minimum, which 

Rb 

it is when the point X coincides with C or the engine is on its inner dead-center. 

When the crank is between the 90- and 180-degree points, the rubbing is in the same 

direction, and the rubbing velocity 



'-^=^""^-1-:)' 



a minimum when the crank is at its outer dead-center. If the connecting-rod be 
assumed to be n times the length of the crank, then for the maximum value above 



y. = r,a(l+l), 



in which all quantities are derivable or known. The rubbing never becomes zero. 
In the foregoing discussion the term "dead-center" has been used. It is obvious 
that the length of the instantaneous radius CX becomes zero when the links 1 and 
2 are in the same straight line. That is, the cross-head has no motion at these 
two instants when the line OP coincides with OC and with its prolongation in OD. 
Power is only exercised or made available when the pressure force makes the piston 
move through a space. When the piston has no velocity, the steam does no work. 
Or, stated otherwise, the pressure of the steam P on an area A can only cause the 
crank to revolve when it has a lever arm or moment to cause such revolution. When 
the sine of the crank angle in Fis^. 366 is zero, there is no leverage or moment to 



THE ENGINE 387 

revolve the crank OP, An engine without crank leverage sufficient will not start 
however powerful it may be compared to its resistance, and an engine in such a 
relation of its mechanism is said to be "on its dead-center" or "on the center." 
There are two of these, the inner dead center and the outer dead center, according 
as the crank-pin is between the cylinder and the shaft, or beyond the latter. 

There is also another dead-center on which an engine will not start to move. It is 
that which is due to the fact that both ports to the cylinder at its two ends are 
covered by the valve in Fig. 346. The design of the valve should not allow both 
ends to be open to steam at once: hence there will be a relation of valve to port 
and to piston position in which no steam nor any turning energy can reach either 
face of the piston. Hence a dead-center even if the mechanism gave a turning 
moment. In engines working expansively, later to be discussed, this latter dead 
point may become a dead period at the end of the traverse in each direction, dur- 
ing which the engine cannot be started from rest by its own steam. 

A fourth deduction is the truth that with a connecting-rod PC of finite length 
the cross-head C has gone further than one-half of its travel when the crank has 
moved 90° from its inner dead-center. In Fig. 366 with an infinite connecting-rod 




Fig. 368. 



this is not the case. This can be shown by two methods. Let the distance from 
the crank-shaft O to the cross-head C on its inner dead-center be the sum of the 
crank-length r and the connecting-rod I (Fig. 367). Then when the crank has 
moved through 90°, the distance OX should be equal to I if the distance XC was 
equal to r or the half stroke of the piston. But plainly OX is not equal to I, since 
it is I cos d, and cos 6 is less than unity: hence XC is greater than r, or the piston 
has moved through more than one-half its traverse in the first 90°. Or the second 
method of Fig. 368 may be used. At the dead-center the distance OC = r + I. 
With C as center and OC as a radius describe an arc through 0. It cannot cut the 
circumference in the lin^ cd through the 90° and 270° points, but at some points 
a and h. Let the crank now swing to the point a. The distance along the lines 
of the mechanism to C will be the line PX + XC. The sum of PX = I and XC 
must be greater than the third side of the triangle PC = r + I. But I cannot 
change in length: hence XC must be greater than r or the half-stroke. This irreg- 
ularity will become greater as the connecting-rod becomes shorter relatively to the 
crank, and vanishes when the crank becomes of infinite length as in Fig. 366. 

258. Effectiveness of the Crank-connecting-rod Mechanism. The 

foregoing kinematic discussion enables a most important and serviceable 
conclusion to be drawn. When a force acts at any point of a mechanism 
and overcomes a resistance at another point, the work done at the two 
points must be equal if friction be neglected. Hence in the steam- 



388 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

engine the effort of the steam PA acting through its path 2 r must be 
equal to the resistance R reduced to the crank-pin and acting in one 
stroke through the space Ttr. If not, the engine must change its velocity 
until there is a balance between the effort and resistance at this new 
speed: because it is also true from the principle of work that the efforts 
in any mechanical combination are inversely as the velocities. If now 
the sum of all the piston velocities with an infinite connecting-rod be the 
area inclosed within the semicircle for one traverse or stroke in Fig. 365^ 
then the sum of all crank-velocities for the same period will be the sum 
of the areas swept over by radius OP equal to the crank-velocity for 
each crank-angle. But each of these areas is equal to the same thing, 

— . Hence they are equal to each other, and the value of the piston 

effort equals that of the crank-resistance in one stroke: or, there is no 
loss of effort in the crank-connecting-rod combination except that due 
to friction.* The deduction of paragraf 3 is, therefore, justified, and 

* This same result can be obtained by the methods of the calculus. Here it is 
simpler to get the area for both semicircles or one complete revolution by getting 
the area of the whole circle from a pole in the circumference. Then r == a sin d, in 

which - is the diameter, and ^ j r^dd = ^ I «^ sin ^QdQ. This is equal to — | sin dbd 
= ^(leos-2»)rf9=2!«- 2! sin 29 T-^- 

4 4 o J (. ^ 



Substituting for a its equivalent 2 r and dividing by 2, 

Area = -^ • 

Or, again, let P denote the pressure on the piston-area, and Y its velocity at any 
point of its traverse. Let p denote the tangential effort on the crank-pin revolving 
in its circular path and y its velocity. These may be uniform or constant, but in 
any case the time may be taken short enough to have them considered constant 
without error. 

If now a circle be drawn representing the path of the crank, and at any point 
the pressure P be represented in direction and intensity by a line parallel to the 
axis of the cylinder acting at that point, it can be decomposed into two components 
at right angles, one tangential and one normal. The tangential component will 
be the effort p at that point, and will be perpendicular to the radius. The normal 
component will coincide with the radius produced. If the tangential component p 
be projected on the piston effort P, there will be three similar right-angled triangles 
produced. From these it will appear that the tangential pressure on the pin will 
equal the piston-pressure into the sine of the crank-angle, becoming equal to it 
at 90° and 270°, and being zero at 0° and 180°. The velocities of crank-pin and 
piston will be to each other in such a relation that the pin-velocity will be a mean 
proportional between the piston-velocity and the projection of the pin-velocity on 



THE ENGINE 



389 



the difference between the indicated horse-power and the net horse-power 
is the mechanical friction only. This answers also the recurrent con- 
tention of the ill-informed that the crank is an ineffective transformer of 
motion or transmitter of effort and something else should be substituted 
for it'. 

Plainly also the shorter the connecting-rod in terms of the crank- 
length, the greater the value of the sin d of Fig. 367 for any crank-angle. 
This means that the pressure from the cross-head upon the guides is 
greater with such short rod than with the longer and therefore the fric- 
tion loss is greater, and the pressure and scraping effects are greater 
which act to expel the lubricant from between the two rubbing surfaces. 
The pressure on the guides does not alternate indirection as at the crank- 
pin, as can be made clear by the four cases of Fig. 369. In case No. 1 the 



No. 1 



No.l 




Fig. 369. 



crank starts from its inner dead-center and rises from the horizontal. 
The piston is pushing on the cross-head with an effort PA and the con- 
necting-rod resisted by the crank is thrusting back in the line of its 
axis T. The resultant of PA and T from zero to 180° is a downward 
force upon the lower guide. In case No. 2 the crank is returning from 
the 180° point to zero and the piston is pulling with an effort PA and 
the connecting-rod is in tension. The resultant is again downward all 
through this traverse. Such an engine is said to ''throw over"; its 
pressure is upon the lower guides only, with minima at each end of the 
stroke. In case No. 3 the crank '' throws under." The piston is push- 



the direction of the piston- velocity, 
from what has preceded, 



(Legendre, Bk. IV, Prop. XXII.) Hence, 



or Pv = pV 

for an instant of time and for any point. Hence, at any point the work given to 
the piston equals that received by the crank, less the loss from friction of joints 
or moving parts. In other words, the crank mechanism is theoretically perfect. 



390 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

ing with PA and the connecting-rod in compression gives a resultant 
directed upward; in case No. 4 the crank is returning over the center hne, 
the piston-rod and connecting-rod are in tension, and the resultant is 
again upward throughout the return stroke. The cross-head can be 
lubricated by a bath of oil on the lower guide; the lower guide springs 
less in a horizontal engine when adequately supported by the frame and 
foundation. Hence " throw-overs " will be usually preferred. The 
locomotive throws under in going forward. In vertical engines it is 
indifferent if the two sides of the frame are the same. When one side is 
open (Fig. 380) then the engine turns so as to thrust against the heavy 
closed side. Engines to reverse frequently or to do equally heavy 
work in either direction must be equally resistant in both directions. 
The resultant R of the four cases must always pass within the contact 
area of the cross-head and guides, else there is a tendency at work to 
cock the cross-head diagonally between the guides and jam it so that it 
will scrape off the oil and run hot. 

359. Dynamic Stresses in tlie Meclianism of tiie Typical Steam-engine. 
The stresses which the engine must undergo and resist and which tend 
to wear it out or injure it are five: 

1. Those due to the pressure coming over from the boiler through 
the pipe. The cyhnder receives these in the form of PA upon the 
piston and the cylinder-cover. The barrel of the cylinder receives them 
as the boiler does (paragraf 25) in intensity given by PD. The 
effort PA tends to pull the piston off the rod, or to shear and strip the 
fastenings: it tends to flex the piston regarded as a beam fixed at the 
center, and uniformly loaded over its area. It tends to buckle or tear 
the piston-rod apart, regarded as a column fixed at both ends, and as 
a tension rod alternately. It tends to shear or strip the fastening of the 
piston-rod to the cross-head, to shear the cross-head pin, and to produce 
the same effects on the connecting-rod and crank-pin. It tends to push 
the main bearing away from the cylinder and to draw it inwards alter- 
nately. When P is known these values are very definite and easily 
computed. 

2. The forces due to the inertia and the living force of the masses in 
piston, piston-rod and cross-head which reciprocate, and in crank and 
crank-pin which revolve, and in the connecting-rod which has a com- 
bination of motions which make its center of gravity move in an ovoid 
curve. The previous paragraf s 256 and 257 showed that the piston 
came to rest in the cylinder when passing its two dead points, and that 
it has the velocity of the crank-pin at or before the 90° point of the 
crank according to the length of the connecting-rod. Hence in the first 
quadrant all reciprocating masses attached to the piston must be 



THE ENGINE 391 

accelerated or have their inertia overcome. In the second quadrant, 
the piston and attached masses must be slowed down and their living 
force absorbed until they come to rest at the outer dead-center again. 
These forces may exceed the PA values of the previous paragraph, and 
affect both cylinder and crank-pin, the latter especially if it is the 
dependence to bring these accelerations and retardations about. The 
energy absorbed in accelerating is given out in retardation less friction, 
so that the principal effect is on the structure which steadies the engine 
and on its bearings and upon the smooth and silent running of the 
engine. The importance of these inertia effects justifies their further 
discussion in a subsequent section. The flinging stress in the connecting- 
rod from the arrest of its mass moving with a lateral component, which 
occurs when the crank passes its 90° and 270° point, are in this same 
class. 

3. The stresses from water in the cylinder, coming over from the 
boiler through the pipe or from condensation in cyhnder or pipes. This 
may produce stresses far in excess of the other two. The clearance 
space between piston and cylinder cover at the dead-centers is inten- 
tionally small: as the piston approaches the end of its traverse the steani- 
valve should close the ports or passages of entry to it and exit from it, 
and in any case will greatly reduce the openings through which water 
might escape. If the volume of water entrapped in the cylinder exceeds 
the volume of clearance and passages up to the valve, such water acts 
by its pi^actical incompressibility as a solid mass to arrest the piston 
before its stroke is completed. At the other end of the chain the living 
force stored in the fly-wheel and the machinery or masses which the 
shaft is driving are all moving at full rotative speed: this aggregate 
applied through the crank-pin finds the mechanism of crank and cbn- 
necting-rod just at that relation of enormous leverage which is given in 
the elbow-joint press at the moment when the links are coming into 
line, and transmits this energy to the compression of the water. If 
the parts receiving this blow are strong enough to resist it, the engine 
stops. If they are not — and sometimes the energy is so enormous 
that they cannot be made so — the piston breaks, the cylinder-cover 
breaks, the cross-head breaks, the cylinder cracks, the bed-plate cracks, 
or pins at cross-head or crank are bent or sheared, the piston-rod parts, 
or the bolts fastening the cylinder cover strip their threads, according 
as one or more of these elements are lower in strength than others. 
Many able designers make a purposedly weakest point in the engine to 
concentrate the breakage here where renewal and replacement are also 
cheapest. The cylinder cover studs are probably the most usual. At 
sea, where water may be thrown from the boilers by rough weather, 



392 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

the cylinders have relief -valves to save them. This danger of practically 
irresistible stress emphasizes the meaning of separators (paragraf 243), 
drip-pipes and traps (paragraf 250) and non-conducting cover- 
ings (paragraf 244). The engine must be started very slowly and 
cautiously to allow water to get away. The design of Fig. 346 is 
particularly excellent from this point of view of water rehef through 
its valve. 

4. The stresses due to sliding contact, rubbing, and friction. These 
must be met by adequate areas in the design so as to reduce the unit 
pressure on them to the least value consistent with meeting other 
requirements, and by such lubrication as shall keep metals from contact 
except with a film of oil between. Such bearing areas are those between 
the piston or its rings and the bore of the cylinder; between the rod and 
its packing in the stuffing-box; between the cross-head and its guides; 
between the pins at cross-head and crank and the connecting-rod brasses 
and between the shaft journal and its bearings in the frame. Adequate 
bearing area and the reduction of unit pressures on areas so as not to 
expel the lubricant belong to engine-design and are in a field too large 
and important to be entered here. Lubrication of such well-designed 
surfaces will be treated in a later chapter. 

5. The stresses due to heating the metal. The engine is bored, planed, 
and fitted at the shop temperatures; in use it is subjected to tempera- 
tures over 300° F. and with superheated steam to a much higher range. 
These heats cause expansions which deform and warp the fitted- surfaces 
when resisted, and cause a superposition of stress. With very hot gas 
the castings grow longer or larger, due to a molecular rearrangement in 
their structure, no doubt; the closely fitted surfaces seize and grip; 
planes warp and wind. Heat also injures the lubricating quality of 
badly chosen oils upon such hot surfaces, changing them into gas in part 
and oxidizing the balance into a gum which prevents easy motion 
instead of favoring it. Deformations, however, are the worst evil, and 
the troubles from them should be guarded against in the design so far 
as possible. Lifting poppet-valves for example are better than sliding 
ones, and cylindrical piston-valves are better than flat ones (para- 
grafs 231 and 417). 

To this same class belong the stresses in the castings of the engine due 
to the impeded shrinkage of such castings when cooHng from the molten 
stage in the mold. An initial stress from this cause may be added to 
the working or heat stresses, and combined they may exceed the resist- 
ance of the material. These give special trouble in cast-iron fly-wheels, 
or when the stress from water comes on. 



THE ENGINE 



393 




f*'~^rU 



AoA,' 



Fig. 370. 



260. Inertia and Acceleration of the Reciprocating Parts of a Steam- 
engine. The velocity diagram of the piston and its attached masses (Figs. 365, 
366) have made it plain that only at or just before the 90° point of the crank-motion 
has the piston the same velocity as the uniformly revolving crank-pin. During the 
first half of the stroke this mass M or weight W 
is receiving and storing energy imparted to it by 
the pressure PA and during the last half this 
energy is being given out or restored to the shaft 
through the crank-pin. If the engine is rotating 
slowly this acceleration and retarding of mass 
may be unnoticed: at high speeds or in the 
absence of a fly-wheel to mask the process, the 
smoothness and silence of the engine may be 
materially affected, and shaking of the engine 
on its foundation and of the foundation struc- 
ture itself may result. If the inertia or resistance to acceleration of the recipro- 
cating parts, reduced to a resistance per square inch of piston-area, exceeds the 
initial pressure P in the cylinder, it is plain that the steam effort did not reach the 
crank-pin until P had overcome this resistance and there was a balance in favor 
of the forward effort. This resistance as the speed grows higher may be enough 
to hold back the engine from attaining any higher speed or running away when the 
load is suddenly taken off. 

It will be remembered that the velocity is the ratio of the space passed over to 
the time taken to move through that space: the acceleration is the ratio of the 
velocity at the end of such a time to the time in which that velocity was acquired.* 
The simplest case will be that of an infinite connecting-rod and a constant crank- 
pin velocity. Then the semicircle of Fig. 366 becomes the velocity diagram when 
the uniform crank-velocity V is the radius. The piston velocities for each crank- 
angle d become (Fig. 370) V^ = V sin 6^ ; the living force or kinetic energy for a 

W 
mass of reciprocating parts M = — at any point of the piston-travel as 4 ^ is 



K.E. = 



WV, 2 ^ WV sin'' 
2gR' 



sin t 



and V = R. 



At a subsequent position of the crank and piston Aj, 

so that since the velocity is increasing from A^ to A2 the increase will be 
(K/E.' ~ K.E.) = 2^, (F,2 - 7,^). 



* With mean velocities. <; = - ; with mean accelerations a = 
infinitesimal, the statements become true for all conditions; or 

ds . dv <Ps 



2< ' 



If the time be made 



394 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



If the motion of the piston from A ^ to A 2 along the diameter be from a distance X2 
from the center to a distance x^, this corresponds to a work done under a total 
pressure P for this purpose of 

Work = P (Xg - x^). 
But since the radius and sines make a right-angled triangle 

so that 

X2' - x,^ = 7,2 _ y^2^ 

Whence the increase of kinetic energy can be written, 

T772 



Increase of K. E. 



29R' 



{X2 X^ J, 



which is equal to P (x^— xj. 
Whence 

P 

which can be written 

if X be the mean distance x = 



2gR' 



{X2 + Xi), 






X, 



'■ of the piston from the crank-center during 

the time in which this acceleration or increase of kinetic energy took place. At the 
beginning and end of the stroke the change from rest to motion is a maximum ; and 
when X = R under these conditions 

gR ' 

This is- identical with the expression for the acceleration due to centrifugal force, 

which implies that the reciprocating parts 
produce the same effect in the crank-pin in 
their actual motion as they would do if they 
were rigidly attached to the crank-pin, 
and while kept parallel to themselves were 
rotated around the engine-shaft. Only the 
components parallel to the cylinder axis are 
under consideration, however, and this is a 
maximum as above at the dead-centers and 
a minimum or zero at the 90° and 270° 
points. It is positive in the first half stroke 
and negative in the second half. Since the difference in the squares of the velocities 
is equal to the difference of the squares of the distances from the crank-center and is a 
constant equal to R^, all triangles whose one side is proportional to such change in 
kinetic energy are similar to each other ; so that a vertical line drawn at the dead- 
center upwards at one end and downwards at the other and with a value to the 

scale of the crank-pin velocity of P = — p- will give the relation of P to such velocity. 




Fig. 371. 



THE ENGINE 395 

Furthermore, a line from the extremities of these verticals to the center of the 
crank-pin will pass through the point of zero acceleration and will be a straight 
line. In Fig. 371 the line aa' will therefore give for any point x the value of the 
acceleration and of the retarding effect for the corresponding crank-angle. 

In these, however, the velocity is in feet per second, which can of course be com- 
puted from the revolutions per minute of the engine, since the crank-pin velocity V 
in terms of the revolutions per minute A'' will be 

,, 2zRN 



60 



Since the pressure Pin the horse-power formula is given in pounds per square inch, 

and is so given all in gauges and problems, it is convenient to reduce both P and W 

to terms of the square inch of piston area. If P and W be divided by A the area of 

P W 

the piston and the quotient be respectively -j = V and -j = a, then 

Since the velocity is in feet per second, R is in feet ib the above. The quantity w 
in massive engines may rise as high as 6 pounds ; in high-speed light engines it may 
fall to 2 pounds. If w be called 3 as an average figure, then 

p = 0.0001 Rm 
RW 



10,000 



If the mean piston velocity be used instead of the uniform crank velocity, the 
latter is greater than the former in the relation 

piston velocity : crank velocity :: diameter : semi-circumference :: 2 :tz, 

whence 

crank velocity = piston velocity X 1.57. 

361. Net Impelling Effort upon the Crank-pin. It is now apparent that 
the full forward pressure of the steam in the cylinder may not reach the 
crank-pin to produce rotation when it would appear to do so, and 
that later there may be more effort than that due to the pressure in 
the cylinder. It is the difference between the steam-pressure and the 
acceleration pressure which actually presses upon the pin. To show 
this graphically let the steam pressure effort be constant during the 
piston stroke. In Fig. 372 let the piston traverse be the base-line SE] 
the pressure of the steam on the piston be uniform and per square 
inch of piston area equal to PS. The cylinder work is proportional 
to the area SERP. Let the acceleration pressure per square inch 
be computed and laid off as a quantity SA acting to reduce the steam 
pressure effort at the beginning of the stroke and to add to it at the 
end. Then if PD = SA be laid off downward from PR, the difference 
will be the net crank-pin effort at each point of the traverse, and the 



396 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



work area will be SECD, shown shaded in the diagram. There is 
lack of full forward effort at the beginning and excess at the end. 
The fly-wheel will store the excess RCO (less friction) and give it 
out to help the deficiency POD at the next stroke. 

It is an added advantage to the expansive working of steam to be 
discussed in a latter chapter that it helps to equalize the periodic 
excess and deficiency due to inertia and acceleration. If the steam 
effort per square inch be not assumed constant but to have a variation 




Fig. 372. 



Fig. 373. 



such as suggested by the curve ABC in Fig. 373 and the work area 
bolow it, and the acceleration pressure be AP laid off downward as 
before, then the net effort on the crank-pin will be the shaded area 
below Pxyz, much nearer a uniform mean. If the crank-pin resistance 
considered uniform be laid on upon the base line EF increased above 

its actual value multiplying it by the factor - to reduce its longer travel 

to that of the piston, the excess of net effort over mean resistance R 
becomes apparent. If the engine mechanism moves vertically instead 
of horizontally, the weight w of the reciprocating parts becomes a 
help and a hindrance alternately upon the crank-pin. If w then be 
reduced to pounds per square inch of piston and laid off above the 
base-lino EF and used additively for one stroke and subtractively for 
the other, the net crank-pin effort is determined still more exactly. 

262. Relief of Crank-pin Stress by Cushioning by Compression of 
Exhaust or Live Steam. It would appear from Figs. 372 and 373 that 
the duty of arresting the moving mass of the reciprocating parts 
places a heavy stress on the crank-pin at the end of the stroke. This 



THE ENGINE 397 

is particularly the case where terminal steam-pressures are high and 
masses or velocities are great. It would be apparent from Figs. 345 
and 346 that if a mass of steam-gas be entrapped on the end towards 
which the piston is moving so as to be gradually compressed in the 
decreasing volume, such compressed gas could be made to act like an 
elastic spring, opposing to the piston a force of gradually increasing 
intensity to arrest its motion and transfer the stress of such arrest 
to the cylinder cover and take it off the crank-pin. Such entrapping 
is effected best by closing the outlet or exhaust passage before the 
end of the stroke of the piston, just enough before so that the rise of 
pressure due to the diminishing volume shall result in a pressure equal 
to that of the incoming steam when the inlet from the pipe shall be 
opened for the next stroke. If the back-pressure when the outlet is 
to be closed be called p^ and the initial or inlet pressure be called jpi, 
and the clearance volume be designated by c and the volume to pre- 
vail when imprisonment begins be called v, then since the cross section 
is constant, these volumes are proportional to the fractions of the 
length of the stroke in each case. By the law of Mariotte for compression 
of gases, 

p&(v + c) = 2?iC, whence -y = — c. 

Vb 

The quantity c is a certain percentage of the cylinder volume and 
therefore of the stroke 2 R]\i may be called 2 Rf. The volume actually 
filled with steam is -y + c when the exhaust is closed and compression 
begins. By substituting the value oi v + c will be determined. If 
the compression be adiabatic the volume will have an exponent greater 
than unity or will give to the equation the form 

V^{v + c)^-" = p, (2 RfY-'\ 

which can be solved by logarithms when pi and p^ are known or 
assumed. Such compression pressures affect the value of the forward 
effort of the crank-pin in Figs. 372 and 373 and should be incorporated 
therein as affecting the forward steam-effort ordinates in the part of 
the curve xyz of Fig. 373 for example. 

Another method to ease the crank-pin stress at or near the dead- 
center is to preopen the inlet valve to the cylinder before the piston 
reaches the dead-center and thus arrest the reciprocating parts by 
pressure from the boiler. This is not as economical of steam as the 
exhaust compression, since the latter makes it unnecessary to fill the 
clearance with new steam at each stroke, and thus lowers the steam 
and water rate. Compression also heats the cylinder walls by trans- 



398 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

mitting thereto some of the mechanical equivalent of absorbing the 
living forces in the form of heat. Compression is caused by exhaust- 
lap on the working edge of the valve, to be discussed later (para- 
graf 425). Preopening of admission is called steam-lead, and will 
also come up for reference under valve gearing (paragraf 428). 

Excessive compression cannot occur with reasonable adjustments of 
the valve-gear and with steam-lead; the opening of the port releases 
excess pressure into the pipe. An ideal diagram of the type of Fig. 373 
would be one in which the crank-pin pressure was constant during the 
greater part of the stroke, falUng to zero at each end and rising to its full 
value early in the next stroke. It might resemble the dotted line curve 
in Fig. 374, in which this ideal is reaUzed. In the broken line curve on 
the other hand the drop below SE to the point C shows that the com- 









\i 



Fig. 374. 



pression has been overdone. The net effect is not a forward push but 
a backward or negative pull in the stroke under consideration from D 
to E. There will be a knock in such an engine due to a reversal of the 
stresses in the mechanism as the piston passes D, if there is any play 
in the connections at the pins, although the reversal of effort at the 
dead-center would not occur. The engine at a higher speed would not 
knock, or with a later continuance of the admission or a higher terminal 
pressure. The dot and dash curve on the other hand is that due to 
too low initial net effort and too high terminal conditions. The engine 
should be run at higher boiler pressure for the mass of its parts at that 
speed, or if the pressure could not be raised, then run it at a lower speed.* 
263. The Turning Leverage or Torque of the Crank. In certain cases, 
as in the locomotive and the motor vehicle, the cylinder must be able 

* For further development of these features, consult Arthur Rigg, "Practical 

Treatise on the Steam Engine. " 



I 



THE ENGINE 399 

to start motion by the intensity of PA acting with the crank leverage, 
independent of the computed horse-power quantities which are created 
when this force moves through a space and creates a work. In a rail- 
road stop on a curve or a grade, or with a motor vehicle in snow or sand 
or mud, the engine must be powerful enough in its turning moment to 
slip its wheels at the lowest speed of piston movement. The foregoing 
discussion shows that at speed the full steam effort does not reach the 
crank-pin at once nor tend to turn it uniformly. This at once suggests 
the two-cylinder engine with two cranks at 90° apart or quartering, so 
that one shall be delivering to the crank its maximum turning effort 
when the other is feeblest. This is done in locomotives universally 
and in many other conditions. This makes it of interest and service 
to lay out the moment of the turning effort to torque and the moment 
of the resistance to such effort around the center of the crank as a pole. 

The diagram of Fig. 373 or Fig. 374 computed as for a connecting-rod of infinite 
length when the engine is at speed, gives the horizontal effort of pressure at the 
crank-pin brass of the connecting-rod for each angle. Then for a finite or actual 
connecting-rod the turning pressure at the crank will be found by two steps: first, 
to project that horizontal or parallel effort upon the oblique line of the connecting- 
rod; second, to decompose that projected effort into two components, one along 
the center line of the crank (which is without turning effect and only produces 
journal pressure) and the other perpendicular to the crank axis or normal to the 
instantaneous radius (Fig. 365) which is the force producing rotation. At any 
point therefore, as at P in Fig. 375, let the horizontal component be p}^ which becomes 
Pc on the connecting-rod. Its normal component becomes p„ on decomposition, 
perpendicular to the radius. The turning moment is i?p„, and varies from R when 
the force is so small as to be negligible up to a maximum when the component 
along the crank-center is zero. This kinematic turning moment may therefore be 
laid out by drawing radial lines from the crank-circle circumference outward, each 
having the value of p^ computed or determined for that crank position, giving a 
curve similar to that of Fig. 365. But the dynamic value of this moment is the 
product of the per square inch value of the piston effort multiplied by the area A 
of the piston, or PnAR, in foot-pounds. The uniform (or varying) resistance 
moment can be similarly laid out. If uniform it will be a circle, and wherever the 
torque curve falls within it the fly-wheel is giving out energy stored when the 
torque curve was outside the resistance. If at any point the torque curve falls 
inside the crank-circle whose radius is R, this means that p„ had a minus value, 
and the crank and fly-wheel were driving the piston with a negative effort in the 
cylinder. 

If instead of using a diagram for the torque of the crank it is preferred to get 
the value analytically for any particular crank-angle, as for starting, for example, 
it will be plain from Fig. 375 that pj^ = p^ cos a 

and nR sin a = R sin 6, 

sin d 

whence sin a = , in which d and n are known. 

n 



400 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

Hence, since pn — pc cos (f> 

and 4) = 90° - (d + a) 

Ph r^^ .^ , . , ph sin (d + a) 

pn = -^ — cos [90 — (6 + a)] = ^ ^ . 

^ cos a ^ ^^ cos a 

If now the engine has two cranks at 90°, the second torque curve will have its 

origin or infinitesimal value for pn at the points E and D, or its maximal values 

where the previous curve shows its least. If three cylinders are used and three 

cranks a still closer uniform value for a mean curve will result, which for any crank- 

1,,,---^^ angle will be the sum of the ordinates of all the 

,'"'' eI/^ \ crank efforts. Four cranks distribute the inten- 

/ y^^^^^^Tiq^^^^ \ sity of the effort on four crank-pins, but if kept 

Y i l^^Ty^7--L\^ ^* 90° intervals do not improve the turning 
A ' ^^ ;' \>'\ ^^^'''a }^-^ moment over the results with two. Better 

I j ' /b balancing of masses, however, may be given, on 

Y j / which this diagram is silent. More than four 
^^.^_L^.^ cranks make multiples of the two and three 

^ arrangement, and while introducing no advan- 

^ ' ■ tages not offered by two, three, or four, they 

make grave and almost prohibitory difficulties in construction and in cost which 
are not returned in advantages. 

264. The Flinging or Slinging Stress in the Connecting-rod. It is 

evident from the foregoing that the longer the crank with a given rotative 
speed, the greater the crank-pin velocity and hence the greater the accel- 
erative effort in passing from a velocity zero to a high crank-pin velocity 
in a given time. This makes it usual to have short crank-radii with high 
rotative speed and low rotative speeds with the large torque of the 
longer crank. This will be taken up again in discussing high-speed and 
low-speed engines, and with short stroke and long stroke (paragraf 280). 
It will be obvious, however, that in passing the 90° and 270° points of 
the crank-pin travel, the mass of the connecting-rod has to be suddenly 
diverted from its tendency to fly centrifugally outward at that point, 
and be drawn back to the center line. This tends to shear and flex 
the rod and to make it vibrate under the shnging effect of its weight 
applied at its center of gravity. Very long rods are sometimes trussed 
in the plane of their flinging tendency, as in beam-engines, since to get 
stiffness by adding metal to the rod is to increase the difficulty to be 
cured. It would lead too far into the field of engine design to discuss 
this topic fully, and would therefore be aside from present purposes; 
but the deduction follows so easily from foregoing determinations that 
those interested may pursue it as follows: 

The centrifugal force developed in a weight w pounds at the end of the crank 
R feet long is F = 0.00034 wRN\ 

If the rod be supposed to be of steel, then for each inch of rod of cross section A 
its weight will be 0.28 A, since steel weighs 0.28 of a pound per cubic inch. Hence 

F = 0.0000952 ARN\ 



THE ENGINE 



401 



At the cross-head the centrifugal force is zero, and is a maximum at the crank- 
pin; it will vary for any small mass of the rod directly as its distance from the cross- 
head, or the diagram fo-r the distribution of the bending and shearing load will be a 
triangle as in Fig. 376, and the force at the plane distant from the cross-head C the 

distance xd will be —r- and the moment of the reaction at the cross-head pin Re X I 

will be 



Hci - -^ X 2 , 



whence 



Re 



Fl 
6 



The shear at x from the cross-head pin will be 
fFZ IFx 



[t-D 



c- 


^\^^ 








F 


Cent, of ^^>J 
gravity , \s^ 




Rc 


,, 


R ■ 1 




\ 


~^\ir» 




' J 7 


1 '-■ 


^l '^ ^ 






1 


/ 3 ^' 






I 



Fig. 376. 



F^ 
21 



which becomes zero when the parenthesis is zero, or when 

Fl 

which is when 

I 

X = ^^ . 

The bending moment is at a maximum when the shear is a minimum or zero ; 
BO that the bending moment M for a section distant from the cross-head pin C a 
distance x will be 



Ma 



Rcx 



\ I ^2^3] 



Mr 



FP 
15.6 



or for its maximum value by substituting for x at Rc 

FP 

If the half-depth of the section be called y in inches and the radius of gyration 
about a horizontal axis through the center of gravity be called p, then the bending 
stress of /will be related to the bending moment 

^™""" 15.6" T"' 
whence by substituting for F its value above; 

0.0000952 RiVH^y 0000061 RmPy 



f = 



RNH'y 



15.6 p' 



180330 p2 



h' 



' The value for/)' for a rectangular section is /o' = — when the depth of the rod is h. 

If the rod be of rectangular section milled on the sides to give it an I section, the 
area is the exterior enveloping rectangle less the removed part; or 

^ 12 {BH - bh) ' 



402 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

The advantage of the I section is th« getting of the maximum for the radius of 
gyration by putting the material necessary for strength as far as possible from 
the neutral axis; and the stress is lessened because p is in the denominator. The 
factor for the area of the cross- section which appeared both in the numerator and 
denominator has disappeared. Since the bending is a minimum as the cross-head is 
reached, the connecting-rod can have the section reduced toward that end. 

In the parallel rod which couples the drivers of locomotives and which always 
remains parallel to itself, the maximum bending moment is at the middle of the rod, 
and will be 

_FP_fAp^ 

M max ~" "o" ~" » 

whence 

RNH'y 
83333p2' 



0.000012 RNH'y 



This is about twice that of the connecting-rod which revolves at one end only. 
Since the bending is a maximum at the middle, it is possible to remove superfluous 
metal from near the two ends, which explains the appearance of bellying, which was 
quite usual until the I section supplanted the rectangular section. 

265. The Accelerating Effort with Short Connecting-rods. The neces- 
sary angularity of the connecting-rod when it is short or when I = nR has a finite 
or small value, for n alters the acceleration values deduced hitherto for the acceler- 
ation effort, or the pressure per square inch on the piston to accelerate the latter 
and attached weights. The piston is not in mid-stroke when the crank is at 90° 
(paragraph 357) and the line of piston accelerations is not straight (Fig. 371) but a 



Repeating Fig. 365 with necessary modifications in Fig. 377, in which is the 
instantaneous center for the finite and infinite rod, but the radius is OC for one 
and OX for the other, it will be apparent that for the shorter rod 

crank-pin velocity : cross-head velocity :: OP : OC, 
while for the infinite rod, parallel to itself, 

crank-pin velocity : cross-head velocity :: OP: OX, 
whence velocity of CH infinite rod : velocity CH finite rod : : OX : OC. 
At the inner dead-center 

OX :0C ::PX :CS ::l:l-\- R, 
which may be written 

== 1 



CS 
PX 



At the inner dead-center these relations would be 
C'S ^ R 

PX' I ' 

The maximum values of the accelerating 
pressure at the two ends of the stroke 
instead of being 

p = 0.00034 wRN^ 
and equal to each other in opposite sense, become for the inner end 




90-a 
Fig. 377. 



p' = 0.00034 wRN^ I 1 + 



I 



-.) 



. THE ENGINE 403 

(Fig. 378), or greater than p; and for the outer end, 

+ / = 0.00034 wRX' (l- -]=bd 

(Fig, 378), or less than p, when the connecting-rod is n cranks in length and n is 
finite .and small. Then intermediate points are found from the curve of velocities 
in Fig. 365 or 377. The point of zero acceleration will be where the tangent to the 
velocity curve is zero, and a line from the crank position corresponding and of a 
length I will cut the center line at the position (/) of the cross-head. Two other 
points will be those where the acceleration is the same for both the long and short 




Fig. 378. 

rod. With the crank center as a center draw arcs tangent to the short-rod curve, 
and where they touch erect perpendiculars to reach the crank-pin circle. These 
will give the 45° and 135° points of the long-rod curve and can thus be located on 
the line aa' of Fig. 371. The curve will resemble Fig. 378. 

To reach the values analytically by computation and without the diagram, let 
the cross-head velocity be v and the crank-pin velocity V in Fig. 377. Then 

V sin (0 + a) 

V ^ sin (90 - a) ' 
and 



,, /sin cos a + cos d sin a\ 

V = V { . 

\ cos a J 

When a is small as it usually is, its cosine is 1, whence 
V = y(sin d + cos d sin a). 



The diagram shows also that 
I 
R 

whence 



= n 


sin 6 

= -: or sin a = 

sin a 


sin 
n 


t9 


= V 


[sin 6 + 


cos d sin 

n 


-) 




= V 


[sin d + 


sin2^)\ 
2n )■ 







The acceleration of the cross-head is the differential of its velocity in the time 

dv 
dt; or fa = Yt Substituting the crank path Rdd for the space, and multiplying the 

space by dt for the time to get the velocity, 

Vdvdt Vdv 



fa 



Rdddt Rdd' 



404 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

which when substituted for v above gives 

whence the value of p for the acceleration pressure with a weight w becomes 
wV ( ^ cos2^\ 

= 0.00034 wRN' f cos 6 + ^^^ ) • 

When the crank-angle d is zero or 180° at the two ends, this value is the same as 
that found by the graphical solution, as it should be. If there are weights of pump 
plungers or levers to be taken account of, these appear in the value for w, account 
being taken of the fact that levers may give different strokes and velocities to the 
parts which they drive from those of the piston. 

366. Concluding Comment. It has been the object of the preceding 
paragrafs to serve as connecting links between the topics of analytical 
mechanics or theoretical kinematics and the practice of the engine 
builder, and to open the way to the more advanced study of engine 
design and the criticism of failures and accidents in the engine-room by 
the advanced student. The treatment must not be regarded as 
exhaustive or complete. The dynamics of the fly-wheel will be treated 
by itself under consideration of this part of the engine construction. 

Before passing to an examination of constructive details next to 
follow, there are certain features of arrangement and certain elements 
determining the selection of engine-types which should first be examined. 



CHAPTER XYI. 

THE ENGINE (Continued.) 

370. Introductory. The arrangement of engine mechanism suggested 
by Fig. 345 of the preceding chapter, and those derived from it by invert- 
ing the kinematic chain are not the only possible or expedient forms in 
which the steam-engine may present itself. There are other points of 
view, some of them matters of personal preference or alleged adapta- 
bility for special uses ; others again with a valid basis of reason for their 
selection. This chapter proposes to discuss the following topics: 

1. The Horizontal Engine, with cylinder- axis horizontal. 

2. The Vertical Engine, with cylinder- axis vertical. 

3. The Inclined Engine, with cylinder-axis inclined to the horizon. 

4. The Horizontal Vertical Engine. 

5. The Direct-acting Engine. 

6. The Beam-engine. 

7. The High-speed and Low-speed Engine. 

8. The Single and Double-acting Engine. 

9. Right-hand and Left-hand Engines. 
10. Center and Sidecrank Engines. 

IL Sundry Special Designs. 

371. The Horizontal Engine. The horizontal arrangement of the 
cylinder-axis is by far the most usual position for factory or mill-engines 
and for power-plants where room or floor-space is not the governing 
condition (Fig. 345). 

The advantages of the horizontal arrangement are: First, convenience 
of access from the ground-level to every point of the engine-mechanism. 
This is a convenience both in operation and in repair. Second, the 
weight of the engine is distributed over a large area for its support. 
This is of considerable moment where earth must be depended on to 
support the foundation, and becomes a critical condition of design 
for boat-engines, where the light draft imposed by shallow water 
compels a shallow and therefore flexible or deflecting hull-structure. 
This is a notable peculiarity of the practice of engine-design for the 
western rivers of America and for the shallow waters of the British 
Colonies. Third, the foundation itself does not require to be so massive 
to hold the engine still and to keep its frame from jar or vibration. 

405 



406 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

The first of these is usually considered the notable advantage of the 
horizontal engine. 

The disadvantages of the horizontal engine are: First, that the action 
of gravity on all masses of the mechanism produces a friction which is 
absent in a vertical cylinder. The spring appliances of the piston which 
are intended to make it fit the bore steam-tight require to have strength 
sufficient to support the sohd piston in the axis of the cyhnder and 
prevent a wearing of the stuffing-box down on the lower side. The 
action of these springs increases the friction. 

Secondly, due to either of these actions or to both, it is supposed 
that there is an excess of wear on the bottom elements of the cylinder 
which causes the bore to wear oval with the long axis vertical. 

While the tendency of horizontal cylinders to wear oval is undeniable, 
it is a fair question whether this may not be caused rather by the spring- 
ing of the guides and a flexing of the frame than by the action of gravity 
upon the piston; and in many stationary engines bolted to foundations 
the change of shape due to expansion by heat not infrequently so 
deranges the alinement of the engine as to cause the cylinder to wear 
unequally. The tendency to wear is also diminished by having the 
area of contact between the piston and its bore large enough so that for 
a given weight of piston the pressure per unit of area becomes so far 
reduced as to make wear inappreciable. A great gain is further secured 
by so selecting the material for the cylinder-casting that it may resist 
wear by abrasion. The difficulty from wearing is further diminished 
by the practice quite usual with heavy pistons of prolonging the piston- 
rod out through the back or head-end through a stuffing-box and with 
or without a back-end cross-head (Fig. 502). This not only supports 
the weight of piston, but serves to guide it effectively in the axis of the 
cylinder. 

272. The Vertical Engine. The advantages belonging to the vertical 
arrangement of the cylinder-axis are the avoidance of cylinder-friction 
and unequal wear, which are the disadvantages of the horizontal engine. 
But of more moment than these is the diminished area in ground-plan 
which is entailed when the length of the engine is up and down. This 
condition has made the vertical engine practically universal for screw- 
propelled ships which are not primarily war vessels, and has given to 
this arrangement its wide distribution in crowded power-plants in cities 
where ground is costly (Fig. 380). 

The objections to the vertical engine are: First, the effort on the 
crank-pin is greater when the weight of the mechanism is acting down- 
wards with gravity than it would naturally be when the effort of the 
steam has to lift the same weight against gravity upon the up-stroke. 



THE ENGINE 



407 



This must be counteracted, because otherwise the effort upon the pin, 
and therefore the speed, would be irregular. It can be done either by 
counterweighting the crank on the side opposite to the pin to which 
the reciprocating parts are attached, or by means of a steam-cylinder 
whose area shall be so calculated that the pressure of the steam shall 
just neutrahze the weight to be overcome; or the distribution of steam 




Fig. 380. 



to the heavy end of the cyhnder can be adjusted so as to develop more 
effort at that end than at the other. The second difficulty is that in a 
large engine the different parts of the mechanism will be upon different 
levels or stories, increasing the number of men required to handle or 
superintend it, and adding to its cost the price of platforms and raiUngs 
(Figs. 380, 382). Third, the engine is not so completely and inflexibly 
secured to its foundation, and a deeper foundation is thereby required, 
or an unequal settling of such foundation will occur, if the concentrated 
load is not sufficiently widely distributed. Fourth, when the piston- 



408 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

rod protrudes from the bottom head of such vertical cylinder the com- 
bined effects of capillary action and gravity upon the condensation 
which takes place around the rod in the stuffing-box and upon the cover 
make it very troublesome to make the stuffing-box tight enough to 
prevent leakage of water. 

273. Direct and Inverted Vertical Engines. The first steam-engines 
operated for pumping and with beams had the cyhnder vertical and 
with the piston going out of the upper cylinder-head. Hence when the 




cylinder was put over the crank-shaft so that the piston-rod came out 
of the lower cyUnder-head, such an engine was called an inverted vertical 
engine. This arrangement will be universal for engines in which the 
power is taken off from the crank-shaft as in electric generators, marine 
engines, rolling mills and the like and where the fly-wheel masses will 



THE ENGINE 409 

be large and the reciprocating masses considerable. Scarcely any other 
arrangement than that of Fig. 380 would suggest itself except for special 
cases. The general advantage of this arrangement is that the moving 
reciprocating parts, which are those whose inertia or living force must 
be taken up by solid connection and for which the crank-pin must 
provide, are held to the ground through the crank-shaft directly secured 
to the foundation. The cylinder has nearly the same strain on it as the 
crank-pin, but these strains are transmitted through the elastic cushion- 
ing action of the steam. The cylinder is not a moving part but may be 
solidly bolted to the vertical members of the frame and anchored to the 
ground. 

For certain uses the inverted vertical arrangement is specially adapted 
by reason of the location of the engine-shaft near the base. It is this 
condition which has made this the typical marine engine (Fig. 381); 
but it is also adapted for any function where the vertical arrangement 
is either preferred or necessary. 

It will again be found the most convenient arrangement for water- 
works pumping-engines where the level of the water in the well or source 
from which the pump draws is either some distance below the general 
surface of the ground or is liable to wide fluctuations. Furthermore, 
where the pumping organ is a plunger of considerable weight or length 
it will naturally be arranged to travel vertically and the steam-cylinder 
which drives it will be inverted vertically above it (Fig. 382). 

The support of the massive pump plunger is inconvenient if it traverses 
horizontally, since it is guided at one end only. Moreover, where floods 
may prevail drowning out the w^ter-works it is convenient to have the 
steam-cyUnders above the highest flood level. In pumping-engine 
practice, where the fly-wheel is only a regulator and its shaft transmits 
no power, the direct vertical type has been used (Fig. 383A, Appendix), 
with the piston-rod passing up from the top of the steam-cyhnder to 
cross-head and connecting-rod above it. This is limited to rather quick- 
moving engines with fly-wheels of moderate weight, and is little known 
in America except for pumping, and with one exception has been 
restricted to factory practice at slow rotative speeds. In European 
shops such engines are often bolted to the wall, and are then called wall 
engines. Where a vertical engine has been desired and the inverted 
type disapproved, either the back-acting design has been chosen 
(Fig. 361) or use has been made of the advantage offered by some of the 
beam mechanisms. 

274. Inclined Engines. A modification or derivative of the horizontal 
engine is met in marine practice with side-wheels, where the desired 
speed of the engine and the limit of speed set by the eflB.cient action of 



410 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




Fig. 382 



THE ENGINE 



411 




Fig.. 384. 



412 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

the paddle-wheel floats upon the water have fixed the diameter of the 
wheel, and hence with a desired immersion, the height of the wheel- 
shaft above the water. To keep the cylinders low down in the hull, 
and lower the center of gravity to diminish rolling, and to free the main 
deck from the room they would occupy, the cylinder axis is inclined to 
the horizon and the piston-rod points obliquely upward. This type 
has been much used in ferry-boat service, and in the sound and river- 
boat designs both of Europe and America. Fig. 384 is the engine of a 




Fig. 385. 



channel steamer, similar also to the general arrangement of the Hendrik 
Hudson engines of the Hudson River. The type is specially advan- 
tageous where a light draft and shallow depth of hull are factors. Fig. 
385 is a water-works pumping-engine for a town of moderate size where 
four water cylinders are to have their motion controlled by one crank- 
shaft and fly-wheel. This gives some of the advantages of the horizon- 
tal-vertical design of the next paragraph as respects the quartering 
cranks and distribution of work, and in general while it does not offer 
the disadvantages of the two other types to the same degree, neither 
does it reap their respective advantages. Fig. 386 is the inclined double 
compound type in use on Long Island Sound. The next type is the 
more modern stationary solution. A few examples for power uses of 
self-contained engines of this style were once made in small sizes but 
are now no longer in the market. 



THE ENGINE 



413 




414 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

275. The Horizontal-vertical Engine. Recent designs of large 
capacity engines have embodied the advantages of the arrangement in 
Fig. 386. One cyUnder is that of a vertical engine and a second is that 
of a horizontal engine. The two connecting-rods act upon a common 
crank-pin on the single crank and drive the shaft. Such an engine is 
called a horizontal- vertical engine. Its advantages are: 

(a) Less area occupied in ground plan than if both cylinders were 
horizontal, and only a very little more than if both were vertical. 




Fig. 387. 



(b) When the engine is compound and massive, the heavy low-pressure 
cylinder is steadied close to the ground. 

(c) The two cylinders act with the turning-moment of one at its 
maximum when the other is at its minimum, as the mechanisms are 
quartering, or 90° apart. The inertia of each engine gives out energy 
to the crank during the quadrant when the other engine masses are 
giving the least. Hence the shaft turns more steadily; or with equal 
steadiness the fly-wheel mass may be reduced. (Compare Figs. 371 to 
375 and paragrafs 261, 263). 

(d) This result could have been gotten by any arrangement of cranks 



THE ENGINE 



415 



at 90° apart, but this gets it without the cost of manufacture entailed 
by a double crank. 

In Fig. 387 of a compound engine, the piping between the two cylinders 
enables a reheating chamber to be easily introduced to dry or superheat 
the steam for the low-pressure cylinder. 

This arrangement is also well adapted for the compression of volatile 
fluids, in those designs where a liquid such as oil is used in the clear- 




FlG. 



ance spaces of the compressor to reduce losses therein to a minimum 
(Fig. 388). A vertical compressor is therefore most serviceable, and 
by this type, which quarters the cranks of the driving and driven 
cylinders, the maximum crank-pin work is received from the driving 
piston at the time when the maximum compression resistance prevails. 
The pump-cylinder can be vertical downward or below the axis of the 
horizontal steam-cylinder to meet the requirements of a water-works 
pumping-plant with plungers and where a wide fluctuation of supply 
level is to be faced (paragraf 273); or again a beam may be intro- 
duced as in the designs of the next paragraf to change the direction 



416 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

of effort and resistance instead of using the crank and pin for this 
purpose. 

376. The Direct-acting Engine. In the typical engine of Fig. 345, 
whether horizontal, vertical, or inclined as in the illustrations selected 
in the previous paragraphs, the power is applied as directly as possible 
to revolve the crank. Such engines are all called properly direct-acting 
engines to distinguish them from the back-acting types such as Figs. 360- 
363. 

It is again used in steam-pump practice to denote the type of pump 
in which there is introduced no rotary mechanism with shaft and fly- 
wheel weight, the steam-piston acting directly upon the pumping-piston. 
In this latter sense it is synonymous with the term non-fly-wheel pump, 
and in the first case it is synonymous with forward-acting engine to 
distinguish it from back-acting. It is unfortunate that the same term 
should have so many different meanings, because in the sense in which 
it is desired to use it here the distinction is to be drawn between direct- 
acting engines like Fig. 345 and those in which the effort in the cylinder 
reaches the crank-pin indirectly through a beam. 

211, Beam-engines. Since the earliest steam-engines were designed 
to operate the rods of mine-pumps, it was convenient to locate the 
cylinder at a little distance back from the mouth of the shaft, and to 
transmit the motion of the piston to the rod which went down the shaft 
or pit by means of a pivoted lever or beam. This beam was usually of 
wood pivoted at the center on convenient bearings, which were in most 
cases supported upon a masonry wall. When the function of the engine 
changed from that of pumping to the continuous driving of a revolving 
shaft the general design was only modified by connecting the outer end of 
the beam by a suitable connecting-rod to the crank-pin of the revolving 
shaft, and it seems probable that the term pitman often and properly 
attached to this organ of a beam-engine mechanism is a survival of the 
early mining term. The earliest steam-engines in America for marine 
use were beam -engines, and the preference of many skilled designers of 
side-wheel vessels for this type of mechanism shows that there are valid 
reasons for its popularity. 

The advantages of the beam-engine mechanism are as follows: 

First, the steam -cylinder can be vertical (paragrafs 271 to 275) in 
cases where the elevation of the cylinder for an inverted arrangement 
or a back-acting arrangement would be inconvenient. Such advan- 
tages as attach to the direct vertical cyhnder are obtained. 

Second, the cylinder and its weight are kept down low bolted to a 
bed or sole-plate, with advantages of low center of gravity and steadi- 
ness in vessels and elsewhere. The shaft and its bearings are also low 



THE ENGINE 417 

down as in a horizontal or inverted vertical engine and with the same 
advantages. 

Third, a long crank arm and a large turning or starting moment, and 
the consequent long traverse of the piston is possible and yet not too 
mucli space in ground-plan consumed. This is a great advantage in 
side-wheel practice and in pumping. In both these cases the number 
of revolutions or the number of reciprocations of the piston must be 
kept low, yet it is desirable that the piston-speed L N (paragrafs 3 and 
282) should be made high in order that the engine may be powerful. 
The beam-engine attains these results in a satisfactory way. 

Fourth, the beam-engine secures a flexibility in the alinement of the 
cylinder-axis in its relation to the axis of the shaft. This is specially 
desirable for vessels of light draft whose hulls cannot be made absolutely 
rigid. 

Fifth, for engines specifically designed for pumping, and particularly 
where several steam-cylinders and work-cylinders are features of the 
design, the beam construction furnishes convenient points of attach- 
ment for these various organs. 

Sixth, where valid reasons demand that the steam-cylinders be 
vertical and the work-cylinders horizontal or inclined, while their 
motion shall be hmited and controlled by a revolving crank and fly- 
wheel, the beam principle lends itself to attainment of this result. 

Seventh, the swinging beam rotating round an axis parallel to the 
crank-pin gives less obliquity to the connecting-rod at many points in 
its alternate push and pull upon the crank than where the end farthest 
from the crank is guided in a straight line. The beam engine of Fig. 389 
shows the four-bar chain of mechanism in its most apparent form. 

It is probable that the union of high piston-speed with slow rotative 
speed, and the advantages which are secured by the combination of 
these two features in a flexible alinement, are the cogent reasons for 
the widespread acceptance of the beam mechanism. 

278. Structure of Beam-engines. Fig. 389 illustrates a typical 
arrangement of an American river-boat beam-engine of the period 
1850 to 1875. The type was practically fixed by the late Charles W. 
Copeland, and the sketch shows the beam supported on a frame of wood 
which has been variously called the gallows-frame or the A-frame, 
from its shape. It will be seen to have been well braced by wooden 
knees. The modern frame is of steel worked up into box-girder forms, 
securing thereby greater rigidity and less weight than was required 
in the wooden frames which they have displaced. 

The beam itself in early practice was a cast-iron girder with the 
metal of the flanges so disposed as to secure the greatest strength and 



418 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

stiffness with the least weight. This gave to the beam the form of two 
semi-parabolas back to back, meeting over the center. The greater 
lightness attained by using wrought iron for tension elements of the 
beam caused the open-work or lozenge beam to be early adopted by 
American designers. Its first use is usually attributed to Stevens. 



Stt-,,k€ /5-' 




liimijajMirkEM^ 



Fig. 389. 

The solid wrought-iron forged diamond or lozenge transmits the alter- 
nating push and pull of the piston by an alternate tension in its upper 
and lower halves and the cast-iron center keeps the beam in shape and 
is exposed to compression only. 



II 



THE ENGINE 



419 



ti';:!::T 




420 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




s)OD CLomnai 



Fig. 391. 



THE ENGINE 



421 



The cross-head at the upper end of the piston-rod either is guided 
in a straight-Une path or is steadied by a Hnkage or parallel motion. 
The linkage is less usual. Two short connecting-rods connect the cross- 
head to the beam, one on each side of the latter to cause a symmetrical 




application of the force. Great care is necessary in the practical 
handling of these short connecting-rods as they wear at the bearing 
surfaces; since if they are permitted to become of unequal length a 
serious cross-strain is brought upon the cross-head, and a twisting 
strain upon the beam. 



422 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

At the outer or crank end of the beam depends the long connecting- 
rod or pitman. It requires to be long when the crank is long, and it 
is therefore usual to brace and truss it with light steel tension-rods 
and king-posts, so that in its ampHtude of swing its own mass should 
not have a tendency to make it fling and flex. 

Fig. 390 shows the form which the beam-engine may be made to 
take for war-ship conditions and where a short stroke and rapid revolu- 
tion of the screw-shaft running lengthwise of the vessel are the condi- 
tions to be met. The vessel is a twin-screw ^ruiser, and the engines 
are arranged right and left athwart ship. There is a space between 
the two shafts for the vertical cylinders and the beam frame, and yet the 
whole engine mechanism is below the water-line. This latter is the 
principal object sought in the design, as otherwise the inverted vertical 
cylinder would have been advisable. Fig. 391 shows the convenience 
of the beam mechanism when pump-plungers and connecting-rods are 
to be provided for as well as the steam-cylinder connections. While 
the inclined -cylinder design permits the straight descent of the plunger- 
rods, it can readily be seen that a successful design could as easily have 
been made by having the cylinders vertical and attached to a longer 
beam, leaving space nearer the center for the attachment of the plunger- 
rods, and one on each side could have been used. It is an advantage 
to give a long stroke to the steam-cylinder to secure high-pistbn-speed, 
but the pump plungers must move slowly to allow easy flow of water 
and unaccelerated through the valves. 

In Figs. 392 to 395 the use of the beam mechanism for the engine for 
economical pumping of large masses of water is presented. In Fig. 392 
the engine is horizontal and is twinned, with one compound engine 
complete on each side of the fly-wheel plane, and with a vertical pair of 
small beams, one for each engine. The beam serves to connect the 
high and low-pressure cylinders to each other, and to secure for both 
the regulating effect of the fly-wheel. The pumping work does not 
go through the beam as in the previous examples. 
• In Fig. 393 the inverted vertical type of Fig. 383 reappears, with its 
advantages respecting the pumps, but the fly-wheel shaft and bearings 
are removed to one side, and the beam takes a tri-angular or three- 
bearing construction in addition to the main bearing or beam center. 
In Fig. 394 the same general assembly type is preserved, but the 
beam loses even a resemblance to any conventional form. 

Fig. 395 reverts to the horizontal type for pumping, and introduces 
the half-beam, or that where the main bearing is not between the points 
of application of the power and resistance, but the beam is a lever of the 
third order and not of the first. The fly-wheel being a regulator only, 



THE ENGINE 



423 



the compression center casting is omitted above the attachment of the 
piston-rod Unk and a triangle of tension rods operates the main connect- 
ing rod. In Fig. 396A in the Appendix for a single or twin-screw mon- 
itor of low-head room and to keep all below the water-line, the beam 
becomes a rock-shaft, with its main bearings in the sole-plate. The 
trunk-piston connecting-rod drives the short arm in the line of the 




Fig. 393. 



axis of the cyhnder nearest to the observer; and the longer arm is far 
enough behind the plane of the cylinder axis to let the connecting-rod 
to the crank clear the cyHnder at the back. 

279. Objections to the Beam-engine. The Side-lever Type. Objec- 
tions to the beam engine are: 

(1) The power is appHed indirectly to the crank-pin when it goes 
through the beam. There are frictions at the beam-center and ar the 
multipHed joints. 

(2) These latter require special care, since if the beam is kept single 
to keep it light, then the connecting-rods must be forked at one end to 



424 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

get hold of pins on each side of it. If the beam is doubled, it is heavy 
and costly. If the rods are forked, it is difficult to keep the effort going 
symmetrically through both arms of the fork. 




(3) The masses of the beam and its extra connecting-rod or rods have 
to be accelerated and stopped if the engine is to go fast at all. 

(4) Extra joints to keep in order and to lubricate. 

(5) In marine practice the inconvenient weight of the high frame and 
the beam at its top, so far above the center of gravity of the hull and 
its loading. 



THE ENGINE 



425 




426 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

(6) The exposure in warships of a vulnerable part above the armor, 
whose destruction is a fatal disablement. 

The beam-engine has been a favorite for shallow draft conditions where 
the hull could yet be made stiff enough to hold up the concentrated 
weight of the engine and its frame. It never has had a vogue for paddle- 
wheel practice in Europe, and has disappeared from transatlantic and 
warship practice with the paddle-wheel. 

The warship and ocean difficulties gave rise at an early date to the 
adoption of the back-acting principle to beam-engines with a double 
beam pivoted below on each side of the frame. From this double beam 
or side lever the connecting-rod or pitman rose to the level of the main 
shaft above the beam. This was the type known as the side-lever 
engine, and was in very general use up to the time when the introduc- 
tion of the propelling screw displaced the side wheel for ocean service 
(Fig. 397A in the Appendix). 

280. The High-speed and the Low-speed Engine. It will be apparent 
from the formula discussed in paragraf 3 that the work capacity or 
power of the piston type of steam engine in the form 

j^p PAXLN 
33,000 

can be made to vary with the value of the factors in the numerator; 
but if certain conventions are observed as to usual limits of these values 
either absolutely or relatively to each other, certain types of engine 
will result from these assumptions. For example, the piston-traverse 
is rarely less than the diameter of the piston, and rarely or never more 
than twice such diameter. The maximum pressure is fixed as a rule 
by the safe boiler-pressure permitted by the material of the boiler 
(paragraf 24 to 26) and its shape. Hence the mean working-pressure 
has also an accepted or usual value. The value of N is apt to be within 
certain limits by reason of the inconvenient losses in acceleration 
(paragraf 260), if it is made too large. Hence when N is large for 
reasons connected with the work which the engine is to do, then the 
weight of the reciprocating parts should be small; but this weight will 

be greater with large values of A and with a long crank arm (- ) since 

the connecting-rod length will vary as the crank-arm of which it is a 
multiple. Two types of engine result, of the same horsepower and the 
same value of P, according as N or the number of traverses or recipro- 
cations is large or small. The one class with a high value for the recip- 
rocations or revolutions per minute will be called high-speed engines: 



I 



THE ENGINE 427 

the other, with a low value for N, will be called low rotative speed, or 
low-speed engines. A high-speed engine is one which makes a large 
number of revolutions per minute. The consequences of this are: 

1. The engine has a small cyUnder= volume because it fills that volume 
frequently each minute. 

2. The small cylinder-volume both in length and diameter means an 
engine light in weight. 

3. A short length of cylinder means a small crank-arm, a short con- 
necting-rod, and an engine short in length. These three conditions are 
the same as to say that to increase A^ diminishes both weight and bulk 
and acceleration losses with a given power. P also has no weight. 
When the engine is to move by its own power as in self-propelling motors 
of any type, this is the important advantage of the system. 

4. When the engine makes a high number of revolutions per minute 
each revolution is made in a fraction of a second, and consequently 
a variation of either effort or of resistance is more promptly met, and 
is less noticeable as compared with the mean effort or resistance of any 
given minute. 

5. The regulating mechanism partaking of the rapid rotative motion 
produces its effect to equalize effort and resistance in a less interval of 
time than with the slower-moving types. 

High-speed engines are those which make over 200 to 250 revolutions 
per minute with engines of two feet stroke or over, up to the 1000 to 
2000 revolutions of small engines for motor vehicles or small boats. 
They are used in locomotive, motor vehicle, electric light and marine 
launch practice, in rolling-mills and street railway power houses. 

281. The Low-speed Engine. In pumping water or air, in marine 
paddle-wheel practice, or where gearing is to be used in transmission, 
the number of revolutions or of traverses should not be high. With P 
fixed in the formula for horsepower, and A^ kept small, the values of 
A and L or the cyhnder- volume will grow larger and an engine of greater 
bulk results, with the disadvantages of this type. 

But it will be clear in inspection that if L be made large, or the engine 
is a long-stroke engine, the product of the two factors Lx N may be the 
same as in the preceding case, and the engine may have its piston-effort 
pass through as many feet per minute in this latter case as in the fastcL' 
revolution type. A distinction must therefore be carefully made 
between the piston-speed in feet per minute and the rotative speed, 
since a locomotive of two-foot stroke at 240 revolutions is moving 
at the same piston-speed as an 8-foot stroke pumping-engine of 60 
revolutions. 

The high-piston speed- value L N keeps the value for A down, with a 



428 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

given horsepower limit and a value for P given. Such engines will 
have a long stroke compared to their cylinder-diameter. 

The advantages of the long-stroke slow rotative-speed type are the 
avoiding of the disadvantages belonging to the short-stroke high 
rotative-speed engines discussed in a previous paragraph. The dis- 
advantages of the high rotative-speed types are : 

1. The rapid alternating of admission and suppression of steam 
through the ports to the cylinder compel large port areas in the design 
of such engines. 

2 . The rapid motion of the piston compels a generous allowance at each 
end between the piston at its dead-centers at the heads of the cylinder. 

These two conditions create a clearance-volume of the cylinder at 
each end which is filled many times a minute with steam which escapes 
at the exhaust without doing work. The clearance- volume will be the 
area of the piston multiplied by the allowance length, which is usually 
a small fraction of an inch. That length and volume will be a greater 
percentage of a short cylinder than the same length and volume will be 
in a long cylinder, and it is filled and emptied more frequently in the 
high-speed engine. 

3. Where the stroke is short the surfaces traversed are traversed 
more frequently and therefore the wear per unit of surface will be 
greater. This holds true for wear at all rubbing-surfaces. 

4. The concentration of friction and pressure upon small areas 
frequently in action upon each other and the high rubbing-speed at 
joints (paragrafs 257-261) compel very close attendance upon such 
engines, because heating and abrasive wear go on with great rapidity 
when once allowed to begin, from the very circumstances of the case. 
These two conditions increase the possibility of expense for maintenance 
and repairs for this class of engines. 

5. These conditions of concentration compel lubrication of such 
engines to be copious to a degree which may be wasteful if safety from 
heating is to be assured. 

6. The foregoing conditions compel a standard of workmanship in the 
matter of fitting, aline ment, and provision for wear which make high- 
speed engines costly to build and successful only when very well made. 

7. The most frequent reciprocations absorb energy in accelerating 
the masses so many times a minute (paragraf 260). 

These objections to the high rotative-speed steam-engine are the con- 
siderations which point to either a moderate or low speed of rotation 
as that to be desired when circumstances permit. 

383. Piston Speed Values in Feet per Minute. Since the product L N 
of the horsepower formula is made up of two factors, a very wide number 



I 



THE ENGINE 429 

of combinations is possible. When LN is expressed in feet and their 
product is less than 200 feet per minute, the engine would be a very low- 
speed engine; from 200 to 400 feet is low; from 400 to 600 feet is 
medium speed; from 600 to 800 feet is moderately high; above 800 is 
high 'speed, and above 1000 is very high. Many forms of valve-gear 
preclude the use of high rotative speed, and such engines are best run 
at speeds not higher than 100 revolutions per minute. In general, when 
the engine turns less than 75 times in a minute it will be called a very 
slow-turning engine; 75 to 100 is slow; 150 to 250 is medium; 250 to 300 
is fast, and above 350 is very fast for steam-engines. Locomotives 
usually exceed 300 revolutions per minute. Small motor-car engines 
and especially internal-combustion engines go much higher than this, 
1000, 1200, or even 2000 turns; but attempts to run engines of con- 
siderable size faster than 400 revolutions per minute have not been 
altogether satisfactory. 

383. Double and Single-acting Engines. Since the numerator of the 
fraction in the horsepower formula is made up of pounds, PA, moving 
through L N feet per minute, it is obvious that A^ is the number of such 
traverses made under the power of the effort PA. If only one of such 
traverses in the two which occur in a complete revolution is made under 
power, then the engine is called a single-acting engine. If both strokes 
in and out are made under power the engine is called double-acting. 
The single-acting engine of a given cylinder- volume is only half as power- 
ful as the double-acting of the same cylinder- volume; or two cylinders of 
the given volume must be used in the single-acting engine to give it 
the same power as that of the single-cylinder double-acting type. 

Historically the first engines were single-acting, having their cylinders 
open to the atmosphere on one side. The steam entered at the closed 
end and displaced the piston, was then condensed, leaving a vacuum 
behind, and atmospheric pressure forced the piston back to its starting 
point. They were defensible for pumping purposes, and where poor 
workmanship and unskilful maintenance were to be expected, because 
the stresses were never reversed as in the double-acting type and pin- 
joints need not be so carefully made nor looked after. The Cornish 
is the only type of large engine single-acting, and this will not be rset 
except for mining, where its slow stroke, governed by the flow of great 
masses of water and the inertia of massive shaft-rods, would justify the 
type. It has no fly-wheel nor crank. 

284. The Cornish Engine. A form of pumping-engine, single-acting 
in type, was early applied at mines in Cornwall, England, and has had 
a considerable popularity for water-works uses and for deep-mine con- 
ditions — for the latter by reason of its convenient solution of the 



430 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

problem of massive pump-rods. The Cornish engine appears in two 
forms. The beam Cornish engine has a vertical cylinder from whose 
top the piston-rod passes to one end of a beam pivoted at its center 
(Fig. 402 A) , to whose other end (which in mine-pumps usually hangs 
over the mouth of the shaft) are attached the pump-rods. The Bull 
Cornish, from the name of its first adapter, has the piston-rods coming 
out of the bottom of the vertical cylinder and directly attached to the 
pump-rods. This compels the cylinder to be located over the mouth 
of the shaft or above the plungers. In some French designs of mine- 
pumps and in some water-works pumps in America, the beam has 
been below the cylinder. Where the pump-rods and plungers have 
not the necessary mass, there will be a weight on the pump end of 
the beam leverage to carry the pumps down and force the water up. 





Fig. 400. 



Fig. 401. 



The Cornish principle is that of forcing the water up in the rising 
main or column pipe by the descent of the rods by their weight. The 
steam-cylinder lifts the rods and overcomes their resistance, but does no 
pumping, as a rule. The water controls the speed of the descent of the 
rods; the steam cushioning of the exhaust (paragraf 262), and the 
absorption of the inertia of the masses of the rods by the resistance 
(paragraf 260) controls the length of the stroke. There is no crank 
nor fly-wheel. Each double stroke is complete in itself. 

385. Operation of the Cornish-engine Cylinder. The cyhnder of the 
Cornish engine has three valves (Fig. 400) : 

1. The inlet- valve (;S), admitting steam. 

2. The exhaust-valve (D), allowing steam to escape, usually to the 
condenser. 



THE ENGINE 431 

3. The equilibrium- valve (E), opening and closing a pipe or passage 
between the upper and lower ends of the cylinder above and below the 
piston when at the upper or lower end. 

The steam- valve and the exhaust- valve will be at opposite ends of the 
cylinder, the steam-valve at the bottom of the Bull engine and the top 
of a beam-engine. The cycle of operation will be as follows: The 
massive pump-rods being at the bottom of their motion and the piston 
at the corresponding end of its cylinder, the steam- valve will be opened 
and the exhaust-valve opened while the equiUbrium- valve remains 
closed. The pressure of the steam overcoming the weight of the rods, 
the piston will move and the rods will be lifted. The admission of 
steam will cease at such a point in the stroke as is indicated by calcula- 
tion and experiment, in order to impart to the rods sufficient living 
force to carry them to the end of their stroke. The exhaust- valve will 
close before the piston completes its stroke, so as to shut in between the 
piston and the head of the cylinder sufficient steam to form an elastic 
cushion strong enough to arrest the piston before it strikes the head. 

Safety-catches or buffers were usually supphed in old engines to 
prevent this accident mechanically if the steam should fail to serve. 

The massive pump-rods being now at the top of their stroke, the third 
or equilibrium-valve is opened, permitting the steam to pass through 
it on its passage to the other side of the piston so as to produce equi- 
librium of pressure on both sides. The weight of the rods causes them 
to descend, displacing the water to be pumped with a speed which is 
controlled by the valves of the pump, and by the extent of the opening 
of the equilibrium-valve. Both steam and exhaust-valve are closed 
during this equilibrium stroke, and the equilibrium-valve should itself 
be closed before the end of the stroke, so as to compress the steam 
between the piston and the head, cushioning the piston and filling all 
clearances with steam at inlet pressure. The cycle begins anew by the 
opening of the inlet and exhaust- valves for the next stroke. 

286. Cataract of the Cornish Pumpmg-engine. It was a feature of 
the Cornish massive pump that it should be able to make few strokes to 
the minute with considerable pauses of rest and inactivity between 
them. The continuous rotation of a fly-wheel was, therefore, excluded, 
and if the pump-rods actuated the cylinder- valves directly, the pump 
would stall with all moving parts at rest and there would be no means 
to open the steam-valve for the next stroke. The working stroke 
must therefore store some energy in the form of a lifted weight whose 
subsequent descent, independent of the engine, shall set the valves for 
the next stroke while the engine proper is at rest. Such weight can be 
most easily controlled by resisting its descent by water flowing through 



432 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

a controlled orifice. Fig. 401 will show such a device in the form which 
is known as the cataract. The main-engine stroke raises the heavy 
plunger P. As it goes up water flows freely in through the valve 0. 
The plunger released from the main engine starts downward by gravity, 
but at once closes, and the water under the plunger can only get out 
slowly through the cock- valve ^, partly open, if the flow is to be retarded 
and take a considerable time. The main-engine is at rest during the 
slow descent of P, which at the end of its fall either opens the valves 
directly or releases detents or catches whereby the valves are permitted 
to open by another force. The cataract principle, using a spring instead 
of the weight of the plunger, has been applied to operate the valve 
mechanism of horizontal direct-acting pumps. As such engines are 
double-acting, the graduating-valve will be in a connection which 
joins the two ends of the cataract-cylinder, and the plunger is replaced 
by the piston which fits that cylinder. It is obvious that in either case 
work is stored by the working-stroke of the main engine and given out 
as desired after the main engine is at rest. 

Other solutions for the non-fly-wheel type of pumping-engine have 
been the auxiliary water-motor, having its valves set by the main engine, 
and whose work was the moving of the valves of the main engine. Such 
engine could not stall, for the main engine had its valves wide open until 
the motor reversed them independently of the stroke or motion of the 
large ro ds . (S ee also p aragraf 149.) 

287. Advantages and Disadvantages of the Cornish Pumping-engine. 
The primary advantage of the Cornish pump is that the motion of the 
water through the valves and pipes is made the controlling element. 
Large masses of water can only be accelerated as demanded by crank- 
motion at the expense of considerable work which is unprofitably 
expended. Second, the masses of the pump-rods serve as a reciprocating 
fly-wheel. Third, the single-acting principle of working enables the 
Cornish pump to work with much greater economy than less carefully 
designed pumping-engines belonging to its earlier period. The duty of 
the best grade of Cornish engine stated in the usual form has been about 
100,000,000 pounds of water raised one foot high by the combustion 
of 100 pounds of coal. Fourth, its abihty to work successfully with 
a very small number of strokes per minute. 

The disadvantages of the Cornish pumping-engine are, first, being 
single-acting it is bulky for a given number of foot-pounds of 
work. The mean pressure in the cylinder cannot be high, because at 
the end of the stroke all hving force of the reciprocating parts must 
have been given out. Second, having no crank to limit the stroke of 
the piston, there is the danger from overstroke either up or down. If 



THE ENGINE 



433 



from any cause the pump-barrel fails to fill with water, the massive rods 
descend unchecked and their living force under these circumstances 
will wreck the engine. Third, the bulk of the cylinder and the masses 
attached to the piston compel an expensive and massive foundation 
greatly in excess of that required by an engine of a different type to do 
the same work. Fourth, the intermittent action of the cylinder compels 
very careful provision to keep it warm between strokes, and condensa- 
tion will be considerable in spite of all care. 

The Cornish engine is now only in operation where it was early 




Fig. 40i 



installed. In water-works such as in New York, Brooklyn and Phila- 
delphia it will not be replaced when its work is done, nor built for 
extensions of service. The economy and convenience of new designs 
have taken away its significance. Fig. 402 in the Appendix is the 
Brooklyn engine, showing the older type with cast-iron beam^ parallel 
motion, extra plunger-weight and buffers. 

288. Single-acting Rotative Engines. The demand for an engine of 
high rotative speed for motor-car and power service which shall be able to 



434 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

be cheaply built with respect to fitting, alinement and wear has attracted 
engine-builders to the single-acting principle. In this type, and par- 
ticularly with an inverted cylinder and trunk-engine mechanism with 
the energy of the steam acting with gravity downwards upon the upper 
side of the piston, it is brought about that the effort of the steam 
through the mechanism is in one direction only. Hence silent running 
is secured at high rotative speed because the strain on the crank-pin is 





m^^m 



Fig. 404. 



never reversed, which will be the occasion for knock or pound in a 
double-acting engine upon passing the centers, unless the adjustment and 
fitting are very perfect and the adjustment of the valve-mechanism just 
right. The danger of overheating bearings is lessened when the adjust- 
ments of fit are of less moment, and it furthermore becomes a matter of 
less risk to make use of high initial steam-pressure in the cylinders. 
Continuous action is secured by putting two cylinders to act upon the 
same crank-shaft. The two best-known single-acting engines of the 
rotative type are the Westinghouse and the Willans. Fig. 403 shows a 
longitudinal section and Fig. 404 a transverse section of the Westing- 



THE ENGINE 



435 



house standard engine, and Fig. 405 a section through the Willans 
cyhnders. The trunk-mechanism is clearly manifest in both designs, 
and the principle which they both represent of securing self-lubrication 




Fig. 405. 



by having the crank-shaft revolve in a closed casing which is filled with 
water on the surface of which floats lubricating oil. The use of pistons of 
different diameters is very convenient in engines of this type, and will 
receive discussion in the sequel. These engines may have rotative 



436 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

speeds between 250 and 500 revolutions per minute without difficulty, 
and have been quite a little used where it was desirable to couple the 
armature of electric dynamos directly to the engine-shaft. The Willans 
engine-section shows the characteristic central valve within the hollow 
piston-rod, and Fig. 404 the possible offset of the piston to one side of 
the plane of the shaft, since the work is done through 180° only. 

389. Kight-hand and Left-hand Engines. In the typical engine 
mechanism of Fig. 345, the cylinder happens to be on the left hand as 
the observer faces it. It might just as correctly have been at the 
right hand. Hence two types originate; one will be called left-hand 
engines when the observer stands in the axis of the engine shaft in 
front of the crank and fmds the cylinder on his left. The other or 
right-hand engine (Fig. 406) will be that in which from the same 
position in the hne of the shaft axis the cylinder is at his right hand. 
The selection of one design or the other will be fixed as a rule by the 
location in the room which the engine is to occupy. The wall will be 
nearer the back of the engine than the front so as to keep the belt or 
generator wires as close theroto as possible, and give an obstructed 
passage from the larger areas of the center of the room to the mechan- 
ism. When such considerations are equal then the choice may be of 
personal preference or whim for the right-hand engine because some 
one is used to it. The right-hand side of a standard locomotive is 
always a right-hand engine and the left-hand side a left-hand engine or 
whenever the cylinder is in front of the engine. When the engine 
drives by a belt from the shaft the belt should be kept near the wall 
for safety and convenience. When the shaft to be driven is located 
behind the cylinder, the engine is said to belt back (Fig. 407). If the 
other location exists, and the belt from the fly-wheel or shaft pulley 
is in front of both engine shaft and cylinder the engine belts forward. 
Since the driving by a belt is always done by the bight of the belt which 
is in tension, it will be plain that the bottom side of the belt should 
do the work rather than the top, since any slack on the returning side 
increases the area of contact between the belt and pulley surface of both 
wheels in this case. When the top drives and the lower bight is slack, 
the belt leaves both pulleys sooner than in the other case. Hence 
when the engine belts back, the crank throws under; when it belts 
forward, the crank throws over (paragrafs 259, 265). 

In the inverted vertical type (paragraf 273) there is no right or 
left type when the frame is symmetrical and the guides and cross-head 
permit the engine to turn equally well in either direction. Here the 
engine should turn clockwise as the observer faces it when the belt 
goes off to the right, and contra-clockwise when the belt goes to the 



f 



THE ENGINE 



437 



-sis- 



RIGHT HAND ENGINS 



tal -^ 



Eh 



-s 



L -^^-H I 



ZT 



LEFT HAND ENGINE 



¥ 



-EB3^ 



Fig. 406 




Fig. 407. 



438 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

left. If, however, the cross-head is guided on one side of the frame 
only (Fig. 380) then a right-hand engine has the guides on the right 
side of the observer as he faces the crank and looks along the shaft. 
Such engines should turn contra-clockwise. A left-hand engine has 
the cross-head guides to the left of the vertical cylinder axis and in 
throwing over turns clockwise. In either case if the vertical cylinder 
were revolved around the crank-shaft until it became horizontal and 
rested on the ground with the cross-head right side up, it would be 
necessary to revolve the right hand to the right, when it would still 
be a right-hand horizontal engine, and the left-hand engine to the 
left, when it would become a left-hand horizontal engine. Both engines 
would be throwing over still. 

The valve gear of the engine will always be driven from the shaft 
or the fly-wheel beyond the first or main bearing. This will place 
the steam-chest for the valve on the cylinder on the right or left of the 
cylinder according as the engine is right or left handed. The term 
is often used for a center-crank engine, symmetrical as respects the 
shaft, to describe the side on which the valve-chest is to an observer 
standing at the head end of the cylinder and looking towards the 
shaft. 

290. Center and Side-Crank Engines. The diagram of Fig. 406 
shows that in both the right-hand and left-hand engine the revolving 
crank is at the side of the line through the cylinder axis, and so also is 
the bearing of that shaft on the bed-plate of the engine. Such engines 
which have crank and bearing on one side only of the axis of the cylinder 
are called side-crank engines. If now the two cylinders of Fig. 406 
be brought nearer until they melted into one, and the two crank-pins 
became one and in the line of the common cylinder axis, there would 
be two cranks, or a double crank with each half symmetrical with that 
axis, and two bearings on the bed-plate, one on each side of the crank 
in the center. This makes the center-crank engine. The side-crank 
type requires an outboard bearing beyond the fly-wheel and usually 
independent of the bed-plate: the center-crank has the fly-wheel usually 
doubled (Fig. 408) and the engine entirely self-contained. The shaft 
bearings must be long and ample since the weight of the wheels over- 
hangs. The mechanism is not so accessible in center-crank engines and 
they will be limited to short-stroke high rotative-speed engines of 
small or low medium power, and for belt drives. The larger, more mass- 
ive engine for generators will be of the side-crank type with outboard 
bearings. The term outboard bearing has been derived from marine 
practice with side wheels where the bearing for the shaft beyond the 
wheel or resistance was carried on guards outside of the hull proper. 



THE ENGINE 



439 



In Fig. 408* the double cranks are coimterweighted and the oiling 
sysieni for the crank-pin is shown. The crank-case is inclosed. The 
center-crank type may be called right-hand or left-hand for convenience 
according as the valve-chest is at the right or left hand of the observer 
standing at the head end of the cylinder and looking toward the shaft. 




Fig. 408. 



391. Sundry Mechanisms and Arrangements. The realization of the 
satisfactory transmission of motion and force by the crank and connect- 
ing-rod has rendered obsolete a number of special designs which have 
been advanced to improve upon the typical mechanism. James Watt 
had to avoid a patent in the crank-connecting-rod combination in his' 
early rotative beam-engines and therefore used the sun-and-planet 
device. A toothed gear was bolted to the side of the connecting-rod 

* Ames engines. 



440 mp:chanlcal engineering of steam power plants 

and meshed into another of the same or different diameter on the engine- 
shaft. The gears were kept in mesh by a Hnl^ connecting their centers. 
When the connecting-rod was alternately pushed and pulled, the rigid 




Fig. 409. 



gear was compelled to roll around the one upon the shaft, and com- 
pelled the latter to revolve, since the other could not. If they were of 
the same diameter the shaft made two revolutions for a single complete 



I 



THE ENGINE 441 

revolution of the rigid gear on the connecting-rod. As soon as the 
patent expired the crank was at once introduced. 

The multi-c3dinder engine, designed either to get a required piston 
area without excessive diameter of cyUnder, or to distribute the weights 
of the engine parts, or to secure more uniform turning moment or con- 
tinuous expansion of the steam in more than one cyUnder, or for other 
reasons, makes a considerable variety of designs departing from the 
simple fundamental type. Some of these have been referred to and 
illustrated and others will be introduced in the later treatment of the 
compound or continuous-expansion engine. The large gas-engine, 
which is often single-acting by preference, has presented a number of 
such types, such as the double-opposed cylinders and the cylinders 
tandem upon a single piston-rod. The inside-connected locomotive 
with the two cylinders between the frames compels a cranked axle on 
one pair of driving-wheels, similar to the multi-cyhnder arrangement 
of the marine engine. In quite small engines or of short crank-arm 
and intended for special service in capstans and winches, the three- 
cylinder design of Fig. 409 eliminates the dead-center, since each crank 
is at 120 degrees from the other two, so that no care is required in 
stopping, and the rotation will start as soon as pressure is on. They 
can be handled from a distance therefore. For compactness these are 
usually single-acting trunk engines, and require little fly-wheel weight, 
but are limited in size and capacity. They make good engines for 
steam-steering of large vessels, in the reversing type. 

The vibrating piston-engine of Capt. John Ericsson (Fig. 457 A) for 
small launches; the square piston-engine (Fig. 698 A); the Colt disk- 
engine (Fig. 699A) are all designs of interest at present mainly histor- 
ical and will be briefly referred to in an appendix. Designers in Great 
Britain and Germany have also proposed mechanisms which have 
sought to attain special results, such as the Musgrave two-cylinder 
engine with triangular connecting-rod, and the swinging fly-wheel on 
a vibrating link for pump-service such as Stannah's. These have 
never become standard forms or been extensively reproduced. 

293. Concluding Comment. The next step after study of these 
general arrangements of mechanism of engines would be the details of 
their construction and organs. Before doing this, however, it will be 
advisable to discuss the behavior of the steam' as a motor force in the 
cylinder and the means to secure economy in its operation, in order that 
the effect of these influences upon the design of such elements may 
be made apparent and their significance in relation thereto. 



CHAPTER XYII. 

EXPANSIVE WORKING OF STEAM. 

295. Introductory. The Indicator. From paragraf 3 and the pre- 
ceding chapters it must have been apparent that the greatest value for 
the output from an engine in foot-pounds when the size and speed of 
the cyUnder have been fixed is given from the formula 

^p PAXLN 
33,000 

when P is the greatest. For when the engine is embodied in metal, A 
and L and 33,000 are not variable and the speed N has a fixed or deter- 
mined value which must not be exceeded. How can the value of P be 
known or measured? 

It is plain that it cannot exceed the reading of the pressure gauge upon 
the boiler (paragraf 171) as a maximum. It may easily be -less than 
this, but how much and at what points in the stroke? 

James Watt devised the steam-engine indicator to give to the eye 
and to record the cylinder-pressure on each face of the piston during its 
traverse forward and back. It consists of a piston of known area 
moving with the least possible friction in a little cylinder, whose under 
side is in communication through as short pipe-connections as possible 
with the end of the cylinder (Fig. 410) . It is usual to make this con- 
nection into the clearance, but at such point that the flow of steam 
through the ports shall not affect the pressure actually prevailing where 
the indicator is connected. This pressure connected on the under side 
of the indicator piston would force it upwards in its cylinder, and 
this tendency is resisted by a spring carefully calibrated with respect 
to the area of the piston, so that it shall undergo certain definite 
deformation under certain definite pressure. It will be apparent then 
that the deformation of this spring will weigh the pressure, and if a 
tracing point or pencil be attached to the piston, it will draw a curve 
which will be the ends of ordinates corresponding to the pressure on 
the indicating piston in terms of the scale of, the spring. If a motion 
of a paper at right angles to the piston motion be provided, a closed 
curve will be made, which will thus record the pressures in the cylinder 

442 



EXPANSIVE WORKING OF STEAM 



443 



at every point of the stroke, if the movement of the paper be pro- 
duced by a Hnkage or mechanism driven from the piston by a positive 
reducing connection. It is usual to reel the paper of the diagram 
upon a barrel which is rotated through a part of a revolution by a 
reducing mechanism driven from the engine cross-head. 

It will be apparent that with a known scale of spring in the indicator 
the mean height of the diagram which it traces will be the mean pressure 
upon the piston. The mean height can either be ascertained by finding 
the area of a diagram with a planimeter and dividing that area by the 




Fig. 410. 



length of the diagram, or the mean height of the diagram can be observed 
by dividing the length of the diagram into equal parts and measuring 
the height in each segment, adding their aggregate together and dividing 
by the number of heights measured. 

It will be further apparent that the lines of the diagram will indicate 
the satisfactory working of the distributing valves, or the reverse, by 
reason of the relation of actual pressures to those which ought to prevail, 
and furthermore the approximation of the curves of effort to those 



444 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



which theory indicates as desirable. The indicator is thus a check on 
the setting of the valves, sizes of ports, friction through pipes, resistance 
to free release of exhaust, excessive condensation, ill-adjusted expansion, 
and the like. 

The errors of the indicator are those due to defective accuracy of 
springs, inertia in the moving parts, which causes them to move further 
than simply to balance the pressure, friction which prevents their 
moving as far as they ought to balance the pressure, and inaccuracy in 




Fig. 411. 

the reproduction on the diagram of the motion of the piston in its true 
relation by reason of defects in the mechanism used to give motion to 
the paper. 

Fig. 410 illustrates a type of such steam-engine indicator. What 
will be the appearance of the diagram which it traces? It will have two 
general forms. 

396. Non-expansive Working of Steam in the Cylinder. If the valve 
admitting steam from the boiler and steam-pipe remain open during the 
full length of the traverse of the piston from one dead-center to the 
other, the indicator piston should rise at the left hand of the diagram 
in Fig. 411 to the point represented by the boiler or pipe pressure on the 
scale of the spring resisting motion of the piston. Then as the piston 
moves to the right boiler steam flows in behind it and at that full pressure 
if the passages are adequate until the end of the stroke, at the right- 
hand end. Then the exhaust- valve should open, with a drop of pressure 
down to that prevailing in the exhaust-pipe, and under that pressure 
the indicator pencil should describe the bottom line towards the left, 
and complete the cycle when the admission-valve opens to let in steam 
for the next stroke. If the calibrated spring is correct and known, and 
A and L are known, then the factors of the formula for one stroke are 

all given PxAxLXl 

ji.F. = , 

33,000 



EXPANSIVE WORKING OF STEAM 445 

and the horsepower is computed by direct measurement from the 
diagram. 

Such an engine is said to work non-expansively, or to use its steam 
non-expansively. It works exactly as it would do if the pipe to the 
boiler were full of water and entered the boiler below the water line. 
Exactly the same work is done as would be done by an incompressible 
non-expanding mass of water forced into the cylinder by the steam 
pressure. The water would be at the same pressure at the end of the 
stroke as at the beginning; and to keep up pressure in the boiler a weight 
of water equal to that withdrawn from the boiler would have to be 
made into steam in the boiler. The non-expansive process in the 
cylinder is therefore a purely pressure process and is not a heat process 
or transfer of heat into work at all. Direct-acting or non-fly-wheel 
pumps and some steam elevators work non-expansively. The heat 
process is in the boiler. How efficient is such a process? 

297. Efficiency in a Heat-engine. The efficiency of any machine or 
apparatus is the degree to which it utilizes the energy put into it. 
Its measure is therefore the ratio of the energy utilized, which is its 
output in work units to the input of energy; or 

Energy supphed — energy rejected Work done 



Efficiency = 



Energy supplied Energy supplied 



Now in the steam-cylinder working its steam non-expansively, a 
weight W of steam entered the cylinder and filled its volume at a 
pressure p^ corresponding in the steam tables to a temperature T^, 
If each pound of steam at T^ can do 778 work units for each heat 
unit, then for a range from an assumed zero of temperature to T^ the 
energy input will be TF X T^i X 778 foot-pounds. When the exhaust 
opened, the weight W left the cylinder at the same pressure and tem- 
perature that it went in. Hence the 

(WTJIS) - {WT,77S) 



Efficiency 



WTJ7S WTJ7S 



or as a heat utilizer its efficiency is zero. 

At the boiler the feed-water came in at T2 and was raised by the 
heat of the fire from water at T2 to steam at T^. Since weights are 
the units used, the boiler raised W pounds of water to W pounds of 
steam, and increased the energy from the beginning of the process to 
the end by adding the heat aggregate necessary. Hence the fire input 
was WT j77S-WT.,77S and the efficiency 

T — T 



T, 



446 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

But the heat or fuel necessary to heat this water was greater as W is 
greater per stroke or per minute or per hour. Henee this method 
of working, while giving the greatest work per stroke burns also the 
greatest weight of coal possible to utilize. Cannot this be improved 
upon? 

The valve-gear of such an engine can be the simplest and cheapest. 
It need only open an admission of steam at one end of the cylinder 
and an exhaust valve at the other and hold these open during the 

















' ^\ " 






' SJ 


Cylinder Volume' 


' 








<? 


-Stroke or Piston Displacement — 


> 






A 


S earn Line 


Cut Off 




B 








vC 


- 









-^ 




H 

Clearance 
Volume ' 


a 

3 


^%,^^_^_^ 


""^^--^_D 


Valve Opening 
or Point of Release 

^Boiler Pressure 

by Gage 


% 


\^\ 




^\ 






Atmospheric 


1 \^ 


Exhaust 




Line y 




a Fr 




'- E 






Absolute 


/ 


Vacuum 


.... ^ 


Line 






Valve Closure 
j or Point of Compression 
k l^r- 



FiG. 412. 



piston traverse. For the next stroke, the admission should be at the 
other end, and the exhaust at the end which has just had the pressure. 

The governing of the speed of the engine can be the simplest since 
a valve to throttle or reduce pressure in the steam-pipe as the load 
lessens or the speed increases is all that is required or possible. 

298. Expansive Working of Steam in the Cylinder. The other 
form of the indicator or work diagram exhibiting the steam operation 
in the cylinder has the form shown in Fig. 412. Here the valve 
admitting steam to the cylinder was not open during the full stroke 
or piston traverse but during a part only. At some point as C the 
valve was closed, either by the design of the valve-gear or by its method 
of operation. Hence while the volume between cylinder head and 
piston is increasing, there is no fresh weight of steam coming into it: 
what is now present in the cylinder will follow the universal law of all 
gases under pressure. It will expand in volume decreasing in pressure 
according to some law of relation between the two. Such an engine 



EXPANSIVE WORKING OF STEAM 447 

works expansively or works its steam expansively. The point where 
the admitting valve closed is called the "point of cut-off": such an 
engine is a cut-off engine. An engine which has the point of cut-off 
variable for different amounts of work to be done will be said to have 
a varying point of cut-off, or to be a '' variable cut-off " engine. If the 
engine itself without human interposing can vary automatically the 
location of the point of cut-off, it is called an " automatic cut-off " 
engine. 

What advantages follow from an adoption of the expansive working 
of the steam? 

399. Advantages of Expansive Working of the Steam. 

1. A reduction in the weight of steam furnished to the cylinder 
per stroke from the boiler. Instead of a volume proportional to A 5 
and the corresponding weight at that pressure, the volume and weight 

AC 

are of the full cylinder volume and weight. 

2. During the part of the stroke represented by CB the boiler is 
not furnishing steam to the engine, and during that time therefore 
heat can go in to the water without any going out. 

3. The mean pressure p^ in the cylinder is less than it was in the 
non-expansive case, since the initial pressure is the same as before and 
the final pressure less. 

4. The stroke is less powerful than it was in the previous system for 
this reason. If the horsepower is to be kept the same as with non-ex- 
pansive working the cylinder-diameter or piston-area must be increased; 
but since the expanding steam is not reduced at once to the low terminal 
pressure, but drives the piston continually, the increase in cylinder area 
or diameter will not be proportional to the lowered mean pressure, or 
compel the same weight of steam to be taken into the volume AC as 
was formerly taken into AB. If, for example, the mean pressure in 
expansive working were only 85 per cent of the full pressure of the 

85 
previous case, so that p^ = p^ , it would only be necessary to in- 
troduce the reciprocal of this multiplier into the numerator to keep 

the horsepower the same, or — ^ A = 1.17 A\ But such mean pres- 

85 

sure is the approximate result of cutting off at one-half stroke. Hence 
the increase is 17 per cent in diameter but the steam used is dimin- 
ished by 50 per cent. Num.erical examples of this result will follow. 

5. There is less weight of steam rejected at exhaust, for although the 



448 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

cylinder is full of steam it is at a lower pressure and weighs less per 
cubic foot. 

6. The less weight and at the lower temperature and pressure at 
exhaust rejects less heat to waste. Hence while external losses from 
radiation remain the same there must have been more heat transformed 
into mechanical work than in the former case. That is, the engine is a 
better heat-engine. 

7. The cylinder has now a thermal efficiency as well as the boiler. 
If the final temperature range above a given zero of temperature at the 
exhaust or point of release of the steam be called T^, then the weight of 
steam W at T^ entering the cylinder and leaving it at T^ makes the 
efficiency 

(T77^i778) - {WTJ7S) T, - T^ 



E 



WT J7S T, 



The lower this terminal temperature the greater the thermal efficiency. 
This carries some interesting conclusions as respects the use of con- 
densing engines. 

8. The increased thermal efficiency and the deduction in number 4 
above result in getting a greater amount of work per pound of steam 
than in non-expansive working. As each pound of water is made into 
a pound of steam by burning a definite weight of coal at a price per ton, 
the expansive working is more economical in cost than the other, when 
a given mechanical work is to be done. Since furthermore the efficiencies 
increase with an increase in T^ when the limit of T^ is fixed, the advan- 
tages of high initial pressures and the compound engine which make 
them available are both suggested. 

9. Governing the speed by governing the point of cut-off or the 
ratio of expansion makes the engine make each stroke with an effort 
proportioned to the resistance. Hence the variation of such engines 
from the mean speed desired becomes less. 

300. Disadvantages of the Expansive WDrking of the Steam. The 
offsets to the above advantages are: 

10. The larger cylinder diameter (No. 4) makes the engine heavier 
and more costly. 

11. The valve-gear to produce cut-off of the steam, particularly a 
variable and automatic cut-off, and yet keep the release of the exhaust 
and its compression constant as is desirable to do make such designs 
complicated and costly (No. 9). Depreciation and interest charges 
increase, and possibly also repairs. 

12. The temperature range from T^ to T^ or to the exhaust tempera- 
ture 7^2 causes the cylinder to cool at the end of the working stroke and 



EXPANSIVE WORKING OF STEAM 449 

further durin th exhaust. Hence when the new stroke begins the 
entering steam at T^^ finds the piston and cylinder head cooler than 
itself, and some steam condenses in heating them up. This condensed 
steam in drops or a mist or cloudy vapor reevaporates into steam as 
the* fall of pressure in expanding allows the boiling point of such hot 
water to be reached. The heat to vaporize the water is withdrawn 
from the metal of piston or walls or from the expanding steam, cooling 
them further. All such absorbed heat is swept out with the exhaust 




Fia. 413. 

steam, and. has to be replaced anew by the incoming charge. This 
process is called that of '^ internal condensation and reevaporation " 
in the cylinder, and it is to diminish it that superheating is intended 
(paragrafs 228-231). 

13. The percentarge of the steam per stroke which fills the clearance 
volume (Fig. 412) is greater than in non-expansive working and con- 
sequently the percentage loss is greater. This is more than offset by 
the gains. 

14. A back pressure on the exhaust or negative side of the piston 
of a given and irreducible value is a greater percentage of the lowered 
mean pressure in expansion than it was of the greater pressure through- 
out the stroke in the non-expansive working. 

15. The mechanical friction of the engine acting in effect as a negative 
or back pressure upon the piston diminishes the net or forward effective 
pressure. When this mean effective pressure is less, the effect of such 
constant back-pressure effort is proportionately greater. 

16. The improper adjustment of the grade or amount of expansion 
with respect to the initial pressure or the length of the stroke may 



450 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

produce so low a final pressure that for part of the stroke there is a 
negative pressure, or one less than the pressure in the exhaust-pipe. 
The fly-wheel must drive the piston during such period; and when the 
exhaust opens, the exterior pressure being greater than that in the 
cylinder, there is a flow backward into the cylinder. In locomotives, 
exhausting into the smoke-box of the boiler, this causes cinders or grit 
to rush back into the cylinders, unless relief valves are provided (Fig. 
603) opening into fresh air. Fig. 413 shows an indicator diagram with 
such a negative pressure loop. It may be said in general that the 
expansion line should never go below the line which represents a pressure 
just sufficient to overcome the friction of the unloaded engine. 

301. Numerical Values of Pressure and Work of Expanding Steam. It 

will be of interest and service to obtain quantitative expressions for the elements 
which enter into the behavior of steam in expanding in the engine-cylinder. There 
are two general laws under which expanding gases like steam may be expected to 
act when the limits are such that no condensation of steam to water will occur in 
the process. If the pressure be taken to be that of one atmosphere on a square 
foot, and be called Pq and observed: if the volume of a pound at zero C. and 
under that one atmosphere pressure be called Vq and the absolute temperature be 

•T) y 

called Tq, then the quantity t-—^ for any gas is a constant and definite quantity and 

-^ 

may be called R when computed and observed. For any other temperature a differ- 
ent value for p^v^ will exist, but in every case 

p,v, = RT,. 

If now T be kept constant, as occurs essentially in an engine which is steam- 
jacketed, 



Pi^i 



P2'V2 



Constant. 



Under this law, the expansion curve is an equilateral hyperbola, referred to the 
lines of no pressure and no volume on the diagram (Fig. 412) as its asymptotes: 
.or points of pressure can be computed along the curve by multiplying the initial 

V 

pressure p^ by the fraction — in this last equation. If the cut-off be at half stroke 

for example in an engine of two feet stroke, the pressure at every six inches would 
be, with initial pressure 100 pounds, 



Travel of piston, inches 
Pressure on piston. . . . 






6 


12 


15 


18 


21 


100 


100 


100 


80 


67 


57 



24 
50 



Similarly if the cut-off be at one-third stroke, 



Travel of piston, inches 
Pressure on piston 




100 


4 
100 


8 
100 


12 
67 


18 
44 



24 
33 



This shows the reduction of pressure at the exhaust (Nos. 4 and 5). 



I 



EXPANSIVE WORKING OF STEAM 451 

The other law of expansion revealed from observation is that the exponent of v 
is not necessarily unity, and will not be so when the temperature is not artificially 
kept constant. The natural way is for the final temperature to be less than the initial, 
so that 

This expansion law is followed in a non-conducting and unjacketed cylinder: 
but as it requires logarithms to use and apply this law to numerical examples the 
other law wall be followed, as the results will be close enough for present practical 
purposes. 

If further the cylinder of the experimental engine be supposed to have a diameter 
of one foot or an area of 112 square inches or | of a square foot, the volume of steam 
when working non-expansively will be 1.56 cubic feet of steam per stroke; the work 
done in that stroke will be 100 X 112 X 2 = 22,400 foot-pounds, or 14,400 per cubic 
foot of steam. 

In the first cut-off case at one-half stroke, the mean pressure was 85 pounds, but 
only 0.78 cubic foot of steam was drawn from the boiler. The work done per cubic 
foot was therefore 

85 X 112 X 2 19,040 o. ^nn ^ ^ a w t ^ 

jr-^^ = — = 24,400 foot-pounds per cubic foot. 

0. /o 7.0 

1 56 
In the third case, the mean pressure was 70 pounds: the volume-^ =0.52 

o 

cubic foot. The work done 

70 X 112 X 2 1M§0_ 30200 
0.52 ~ 0.52 ~ '^^'^^^ 

foot-pounds per cubic foot. The method for computing the mean pressure will be 
given in pargaraph 309. It appears therefore that the foot-pounds per pound of 
steam would be as 

14,400 : 24,400 :: 30,200 :^100 :: 170 : 210 

if the non-expansive type be taken as the standard. Earlier cut-offs at -5- and at 
tV of the stroke would give mean pressures of 52 pounds and 33 pounds and corre- 
sponding values of 37,300 and 47,400 foot-pounds per cubic foot of steam. 

But the disadvantages numbered 14 and 15 should be allowed for. An engine 
in which the expansion curve runs down to the pressure level of the line of back- 
pressure is said to have "complete expansion." If the back-pressure line was at 
zero pressure, or that of the complete vacuum, the theoretical values above would be 
reached. Where the vacuum cannot be perfect, or where the exhaust-pipe is of 
moderate dimensions and opposes a frictional resistance, these conditions cannot be 
reached. Hence it will be worth while to assume values for this back-pressure of 
practice and again tabulate. Table XIV results. 

The back-pressure is subtracted from the mean forward pressure to get the mean 
effective pressure, and the difference multiplied by 2 X 112 to get the foot-pounds 
per stroke. This is again divided by the weight of steam admitted at that ratio 
of expansion. 

The back-pressure figures correspond respectively to: 

Column No. 4 — Ideal conditions. 

Column No. 5 — The condensing'engine with no friction allowance. 

Column No. 6 — The non-condensing engine with no friction allowance. 

Column No. 7 — The non-condensing engine with ten per cent friction allow- 
ance. 



452 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

In comment upon the foregoing computations, it should be noted that the lowered 
back-pressure of the condensing engine gives it an advantage over the non-con- 
densing engine at all points of cut-off; that to cut-off earlier than one-fifth in the 
non-condensing engines begins to diminish the work per cubic foot at this pressure, 
but the difference is not very great when friction is not allowed for, and disappears 
when friction is taken account of. The work per cubic foot at -^ cut-off in such 
engines is less than the non-expansive work. It will be seen later again why the 
cut-offs earlier than one-half in such engines are not advisable for other reasons. 



TABLE XIV. 

WORK PER CUBIC FOOT OF STEAM EXPANDING WITH BACK-PRESSURE. 



Cut-off in Fraction 


Mean 

Pressure 

Computed. 


Volume of 
Steam Ad- 
mitted. 


Work Done per Cubic Foot of Steam. 


of the Strolie. 


Back-Pressure being in Pounds. 


Column No. 1 


2 


3 


4 


5 


6 


7 


No cut-off 

One-half 


100 
85 
70 
52 
33 


1.56 
.78 
.52 
.31 
.16 


Pounds. 
14,400 
24,400 
30,200 
37,300 
47,400 


3 
13,900 
23,600 
28,900 
35,200 
43,100 


17 
11,900 
19,500 
22,800 
25,100 
23,000 


27 
10,500 
16,700 


One-third 


18,500 


One-fifth 

One-tenth 


18,000 
8,600 



302. Weight of Steam entering the Cylinder at Different Initial 
Pressures. Steam per Horsepower per Hour. It will be apparent 
that with a given cylinder-volume filled at each stroke with steam 
of differing pressures the work of the weight will differ, and their rela- 
tion to each other becomes of interest. If the same engine of one 
foot diameter and two feet stroke be taken and the cut-off be assumed 
at one-third stroke, then the cylinder volume filled from the boiler will 
be per stroke, 

112 2 14 , . , 

■ X - = — = 0.52 cubic foot. 

114 3 27 



If the engine turn at 100 revolutions per minute, the volume per 
hour = 0.52 X 100 X 2 X 60. To get the weight per hour, the steam 
tables must be consulted to find the weight of a cubic foot of steam at 
the pressure existing at the moment of cut-off. The mean effective 
pressure multiplied by the area and by 200 X 2 and divided by 33,000 
gives the horsepower. Hence for the assumptions Table XV 
follows. 



EXPANSIVE WORKING OF STEAM 



453 



TABLE XV. 

STEAM PER HOUR AND PER HORSEPOWER AT DIFFERENT PRESSURES. 



1 


2 


3 


4 


5 


6 


7 


8 


9 


Initial 
Pressure p^ 


Mean 
Pressure Pm 


Back- 
Pressure 
147+2.3 


M.E.P. 


I.H.P. 


Volume of 

One Pound 

in Cubic 

Feet. 


Weight of 

Steam per 

Stroke. 


Weight of 
Steam per 
Hour, W. 


W 

1 

Col. 8 

Col. 5. 


140 

120 

100 

80 

60 

40 


98 
84 
70 
56 
42 
28 


17 
17 
17 
17 
17 
17 


81 
67 
53 
39 
25 
11 


•110 
91 
72 
53 
34 
15 


3.2 
3.7 
4.4 
5.5 
7.0 
10.3 


0.162 
.140 
.118 
.095 
.075 
.051 


1960 
1690 
1400 
1150 
880 
610 


17.8 
18.5 
19.4 
21.7 
26.0 
40.0 



This indicates plainly the economy in the use of higher pressures 
with a fixed cut-off in non-condensing engines, cushioning and clear- 
ance being neglected, and that such an engine is less efficient . at low 
loads than at the higher. 

303. Cut-off and Ratio of Expansion. Most Economical Point of 
Cut-off. It will appear from Fig. 412 and the law of Mariotte that the 
expansion of steam after the point of cut-off from the volume v^ to 
the final volume v^ will give a ratio of increased volume or of expansion 



which if denoted by r will give 



rv^; or, r = 



a quantity always 



greater than 1, since v^ is greater than v^. The point of cut-off in 

terms of the piston stroke -Uj is — ' Hence the ratio of expansion is the 

reciprocal of the point of cut-off. It is convenient in calculations to 
use the ratio of expansion and avoid fractional values. 

The conclusions of the previous paragraf have shown that it is not 
desirable to have the terminal pressure less than a given value, fixed by 
the back-pressure, either actual or assumed to cover friction of engine, 
condensation water, and other losses. Hence if the initial or boiler 
pressure be fixed and the terminal pressure also determined, the point of 
cut-off and ratio of expansion become fixed, since, 

whence 
which gives 



P2 'Pv . 
P2 Exhaust pressure + friction -h condensation 



P2 
Vi 



Initial or boiler pressure 



454 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

The ratio of expansion being the reciprocal of this is 

^ . Initial pressure 

r = ratio of expansion = • 

Total resisting back-pressure 

For a non-condensing engine, this back-pressure will be made up of 
17 pounds from the vacuum for the pipe resistances and 20 pounds 
for engine friction and other losses, or 37 in all, in smaller engines. 
In larger condensing engines the value of Willans is 25, made up of 
17 -f 8, and is representative of experience. If these assumptions 
be applied to a case using 100 pounds 'of steam as initial pressure, the 
corresponding values for r will be as in Table XVI when various 
total back-pressures are taken. 



TABLE XVI. 

VALUES OF RATIO OF EXPANSION IN ENGINES WHEN p^ = 100. 



Maximum Work in 
Terms of 



Indicated work 
Net or brake work 
Net brake work 

Indicated work 
Net or brake work 
Net or brake work 

Indicated work 



Indicated work 



Will be obtained per 
Pound of 



Indicated steam 
Indicated steam 
Actual steam used 

Indicated steam 
Indicated steam 
Actual steam used 

Actual steam used 



Actual steam used 



By making 

V, 

— equal to 



100-T-17=6 ~^ 

100 

100- 



27=3.7^ 
37=2. 7j 



100-^ 3=33 

100-^17=6 

100-^27=3.7 

100-^25=4 
100^19=5.5^ 



Condition met by 



Non-condensing engines 



Condensing engines 



Willans' rule 
Emery and Loring, 

U.S.N, tests, 1874-75 



The historic Loring and Emery tests would give the back-pressure value in terms 



of the initial pressure p^ = 12.5 + 



The Gately and Kletch test in 1884 on a 



Corliss simple engine gave a condensation value of 0.08 pi, when non-condensing 
and a value of 0.19 condensing to be added to the fluid and engine friction back- 
pressure. 

John Perry* proposed the rule that the internal condensation as a factor of the 
indicated steam should be computed by a formula 



Steam not accounted for 
Steam per indicated diagram 



y 



K 



1 + r 
dVn 



in which d is the cylinder diameter in inches, n' the number of strokes per minute, 

and r the ratio of cut-off. K for non-condensing engines has an average of 15, with 

a best value of 5 in a well-drained jacketed cyUnder with four valves, and rising to 

* The Steam Engine, London, 1902, MacMillan and Co. 



EXPANSIVE WORKING OF STEAM 455 

30 in a cheaper slide-valve engine badly drained and unjacketed. For the con- 
densing engine, he introduces the initial pressure under the radical in the denomi- 
nator, and the average factor is 120, with corresponding limits of 50 and 300. 

An exhaustive test to obtain experimental values of the best point of cut-off 
from the horse-power formulae would cover trials for water-rate when 

1. The initial pressure is made to vary, speed constant, cut-off constant. 

2. Cut-off varying, initial pressure constant, speed constant, 

3. Speed varying, initial pressure constant, cut-off constant. 

4. Speed constant, initial pressure varied with the cut-off so that the terminal 

pressure shall be constant, or, —■ = K, in which .K shall have one of the accepted 

values, say 25. If these results be plotted in curves upon a diagram, it will be 
found that the varying pressure and varying speed tests plot in a straight line on 
indicated horse-power abscissae and weight of steam per hour as ordinates. The 
other two will be curves. The tangent to such a curve will be the water per horse- 
power, from the significance of the coordinates, and it will be greatest for the 
smaller loads. It is only with varying cut-offs that there is a load of maximum 
efficiency. In multi-cylinder or continuous expansion engines, where the expan- 
sion is great in any case, there is not much gain in economy in cutting off early; 
or there is a considerable range of load with the same economy. In a single-cylinder 
engine the gain by cut-off regulation is greater than with the multi-cylinder engine, 
and particularly with the Ughter loads. 

A rule of some acceptance* is to make the ratio of expansion 

r = .42 v^, 

the pressure being counted from vacuum to apply both to condensing and non- 
condensing engines. 

304. Governing in Non-expansive Engines or with Fixed Cut-off 
throttling governing. It will be apparent from Fig. 411 that in 
engines taking steam full-stroke the condition of that diagram and 
with that initial pressure is the full-load value, and cannol be exceeded. 
The only variation with a fixed boiler pressure is downward. A less 
load of resistance must be met in the cyhnder by lowering the height 
of the diagram or the value of sucri initial pressure. This will be done 
by partly closing the valve between boiler and engine, and thus 
throttling the flow of steam by changing the pressure energy into 
velocity through the reduced area of the valve-opening and trans- 
forming some heat into work at the constricted point. 

If the engine has a fixed cut-off, not variable by hand at will while 
the engine is running, the same state of affairs exists. The area of the 
work diagram or the value of the mean pressure must be reduced here 
also by lowering the height or value of the initial pressure. Gov- 
erning appliances which act to control the engine speed by throttUng 
or reducing the initial pressure are called " throttling " governors, or 

* Buckeye Engine Company, Salem, Ohio, 



456 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

such engines are throttling engines. Fig. 415 is a type series of super- 
posed work or indicator diagrams to illustrate practically fixed ratio 
of expansion but a varying initial pressure by throttling action. 

The arguments for the fixed cut-off type with throttling variation of 
initial pressure are: 

1. The engine is cheap to build and to buy. The valve-gear for 
distribution will be simple and therefore inexpensive, and the governor 
controlling pressure only will be extremely simple, and its valve need 
not be comphcated. 

2. The effort of the steam to drive the piston will be exerted through 
a considerable portion of the stroke. Hence there will be less inequality 
in the steam effort at the beginning and end of the stroke. 




Fig. 415. 



3. The effect of driving the steam through the throttling- valve or 
orifice is to bring about the equivalent of a superheating of the steam. 
The pressure on the boiler side of the valve is greater than that on the 
cylinder side. Hence if the steam were saturated at the higher pressure 
it will have a temperature on the low-pressure side higher than belongs 
to that pressure, and is therefore in a superheated condition. This has 
a tendency to dry out moisture in the steam and to diminish condensa- 
tion in the cylinder. The heat corresponding to friction in the throttle- 
valve area must also appear in the form of heat, some of which serves 
to heat and dry the steam. 

4. The throttling-engine for these two latter reasons is likely to 
suffer less from cylinder-condensation. The diminished range of tem- 
perature between the two ends and the relatively higher terminal 
pressure are the reasons for this. 

The arguments against the throttling system can only be weighed 



EXPANSIVE WORKING OF STEAM 



457 



when such engines are in competition with the class using steam expan- 
sively, and the discussion must therefore include the considerations 
of the preceding paragraphs and be viewed in their light. Independent 
of these are the following disadvantages: 

5. 'It is not as sensitive as the cut-off engine to instantaneous varia- 
tion in the resistance. The control by throtthng can only take effect 
in the cylinder at an interval after the governor has acted to throttle 
the steam or to open the valve wider. The engine meanwhile has had 
a chance to make at least one stroke under the conditions which pre- 
vailed before the change of condition was announced to the governor. 

6. The throttling-engine does not regulate as closely to uniform 
speed as the cut-off engine. The reason for this is partly that explained 
in the preceding sentences, and partly because the method of controlling 
by the motor fluid in bulk cannot be expected to be as exact as when 
the control is exerted immediately upon each reciprocation of the 
piston. 

305. Governing in Expansive Working of Steam. Automatic Cut- 
off Engines. The principle of expansive working of the steam in the 




Fig. 416. 



cylinder lends itself so easily to solve the problem, of varying the effort 
as the resistance varies, that this becomes a prime factor among the 
advantages of the system. The valve-gear for expansive working 
can be so easily made to cause the point of cut-off to vary by action 
of the governor, that the variation in cut-off by load can become 
automatic without great entailed expense. Fig. 416 shows the super- 
posed diagrams of a succession of four strokes with varying resistance. 
The smallest area is a card of practically no load. The cut-ofT suc- 
cessively grew later as the resistance increased. 



458 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

Governing by varying the cut-off point without reducing the initial 
pressure offers the following advantages: 

1. The effort is controlled per stroke of the piston. Just enough 
steam is admitted into the cylinder to do the work of that stroke. 

2. For this reason the engine is sensitive immediately to variations 
of the resistance. 

3. It is more certain to be kept by the governing appliance at the 
uniform or fixed speed, since a variation caused in the governing 
appliance operates immediately to control the admission for the next 
stroke. 

4. The full energy present in the elastic tension of the steam as it 
comes from the boiler is exerted upon the piston without undergoing 




Fig. 417. 



the loss from throttling. This may or may not be considered an 
advantage (see paragraf 304 above). 

The disadvantages on this same plane are: 

5. The design and complication of valve-gear to provide for properly 
varying the admission. 

6. This complication usually makes the engine costly to build and 
to buy. If closeness of regulation without the intervention of human 
agency is not worth paying for, the superior economy of the automatic 
cut-off engine does not always pay the interest on the difference of 
first cost. 

The automatically governed variable-cut-off engine secures the 
advantages of expansive working in economy of water rate, but carries 
with it the disadvantages attaching to that principle as practically 
carried out. For example let two actual cards be superposed, one of 
each class as in Fig. 417, assumed to have each the same M.E.P. with 
the terminal pressure 37 for the throttling card A and 27 for the cut-off 



EXPANSIVE WORKING OF STEAM 459 

card B. The weight of steam rejected at oxhaust was that of a given 
final cyUnder volume at 37 pounds pressure in one case and 27 pounds 
in the other for the same work done. The water rate will be 31 pounds 
per I.H.P. per hour for the throttling-engine, and 23 pounds for the 
cut-off, or an apparent loss of nearly 29 per cent over the better per- 
formance by the throttling method. The disadvantages will bring 
this down to 20 per cent or below. The lower terminal pressure causes 
less heat to be rejected into the exhaust, and reaps the full advantage 
of having as great a difference between the initial and final pressure 
and temperatures of the steam in the cylinder as is consistent with 
doing the foot-pounds of work required for that stroke. 

The disadvantages of the cut-off engine are the contradictories 
of the advantages of the non-expansive engine: 

7. There is a wide difference in the pressure and effort at the two 
ends of the stroke when the engine is working with an early cut-off. 
This compels weighty reciprocating parts and a massive fly-wheel to 
take care of these wide variations, and to give out in the latter part of 
the stroke the excess of work stored in it at the beginning. 

8. The lower value for the terminal temperatures and pressures 
increases the amount of cylinder-condensation by reason of the better 
opportunity for the evaporation of moisture present in the cylinder 
either mechanically entrained or as the result of radiation or the 
doing of work. The evaporation of such moisture under reduced 
pressure makes the demand for the necessary heat for vaporization from 
either the working steam or the metal of the cylinder. It is this condi- 
tion which accounts for the result experimentally found, that in non- 
condensing engines, such as the locomotive, it does not pay to carry 
the expansion further than is given with the cut-off at one-fourth of 
the stroke. 

9. It may happen when the engine is very lightly loaded that the 
cut-off will take place so early that the final volume of the cylinder 
will be greater than that which the volume of steam admitted would 
fill at the pressure of the exhaust stroke. The line representing 
pressures will therefore cross the line representing the return-stroke 
before the stroke is completed, forming a loop at one end (Fig. 413). 

WeigM should also be given to the service conditions, because in 
many classes of work in power-house service the variation of resistance 
is so wide and so rapid that it would be inconvenient or impracti- 
cable to depend on human quickness of perception to provide for it. 
On the other hand, where the effort is constant, as in pumping, or is 
progressively varying, as in hoisting from deep mines, and in railway 
and marine practice, the other method of regulation is close enough to 



460 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

be satisfactory, and particularly where the engine-runner must be in 
attendance in any case. The automatic cut-off engine is usually the 
more economical of the two, but it is usually better built in every way, 
and such excellence of construction would explain some of its economy, 
by diminishing leakages and losses in friction and back-pressure. 

306. The Condensing Engine, with Lowered Back-pressure. The 
discussion of expansive working in the preceding paragraphs has made 
it clear that it would be of advantage to diminish the back-pressure upon 
the piston. When the engine exhausts into the atmosphere, the pressure 
therein of 14.7 pounds per square inch above a vacuum precludes 
getting much below 17 pounds for such back-pressure, on account of 
friction in passages, valves and pipe with its fittings. If, however, the 
engine could exhaust into a vacuum chamber when the pressure 
approached zero of pressure, the advantages of such lowered pressure 
could be secured, less the drawbacks of the mechanical apparatus to 
create and maintain the vacuum. The properties of steam and of water 
make it easy and simple to create this lowered pressure in a closed 
vessel from which the air can be excluded, since by cooling the steam or 
the vessel below 212° the tables show that the steam cannot remain as 
steam but must go back to water to such an extent that only the 
remaining vapor can remain steam at such lowered temperature. The 
change to water of so large a volume of steam produces a volume filled 
only with water vapor at the corresponding low tension. This is a 
vacuum, therefore, of varying degrees of completeness according to 
the temperature. 

To maintain this vacuum is a separate process when the vacuum 
chamber is of limited volume. It tends to fill with the water resulting 
from the condensation of the steam, and this water has to be gotten 
out, under the most difficult conditions, since the pressure outside the 
vacuum chamber is greater than that within it. 

The lowering of the temperature in the vacuum chamber will be done 
with the cheapest available cooling medium. This will be water, with 
the high specific heat of unity. It must be paid for, either in a tax, or 
in the interest on the cost of the plant which brings the water to the 
condensing vessel or " condenser " and its operation. If an infinite or 
indefinitely great quantity of water can be used or brought, the water 
will not be sensibly raised in temperature in cooling the condenser and 
the steam. If the water must be handled by pumps or similar apparatus 
it is best to reduce the weight of water, and allow the temperature to 
rise during the cooling process. Hence although the water may be at 
60° F. on an average through the year, the condenser temperature will 
average 110° to 130° F. for these reasons. Air can be used to cool the 



EXPANSIVE WORKING OF STEAM 461. 

condenser by causing cooler air to blow upon a sufficient contact surface, 
but it is much less effective per unit of such cooling surface. 

The advantages of the condensing engine are both thermal and 
mechanical. Among the thermal advantages are: 

1. 'The greater thermal efficiency referred to in paragraf 297 result- 
ing from the lowered value of T^ in the formula. If it can be possible 
also to raise the initial pressure as in the dotted lines of the left hand of 
Fig. 418, the theoretical efficiency is further increased. 

2. This is accompanied with more effective realization of the thermal 
advantages of expansion. The discussion of paragrafs 302 and 303 
showed that lowered terminal pressure increasing the ratio of expansion 
made less weight of steam per horse-power per hour, and hence less 
weight of coal to make the steam per hour. Fig. 418 illustrates to the 
eye the gain of utilization of the intrinsic or potential energy in a given 



ao(H 

80 
60 




G 



Fig. 418. 

weight of steam, if the exhaust need not be opened after a traverse to 
DF only, but the stroke continued by increasing cylinder volume until 
the atmospheric pressure line EG was passed and a terminal pressure 
reached which was about 10 pounds above zero, and the exhaust return 
back-pressure be only about 3 pounds. With a given boiler pressure as 
at H the same net forward effect is produced as though the initial 
pressure had been increased to A, so chosen as to give the same increase 
of area as that secured at the bottom of the card by lowering the back- 
pressure. 

3. This results in a gain in heat consumption or in fuel saving in one of 
two alternative ways. Either the same work is done in a smaller 
condensing cylinder which is done in the larger non-condensing cylinder; 
or in a given Cylinder condensing the cut-off can be earlier than in the 
non-condensing. In either case less indicated steam is used and less 
coal per I.H.P. Fig. 419 shows two superposed cards of equal area and 
equal work in a given cylinder for the two cases. The dotted line is the 
card of work done above atmosphere. The full line shows that the 
cylinder volume need only be filled i- of its volume to do the same work 



462 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

with expansion below atmosphere, as the non-condensing requires a 
volume of -J- of the whole to do. This gain, if all realizable, would be -^-^ 
of the steam weight per hour" or 13 per cent under the pressure con- 
ditions assumed. 

4. A heat saving results from impounding and storing in a hot-well 
the hot water resulting from condensing the steam. This can be used 
as boiler feed-water (paragrafs 146 to 151), doing away in part with 
apparatus to preheat the feed-water (paragrafs 225 to 227) and 



40 lbs. spring 




Atmospheric Line 



L 



Fig. 419. 



lessening the heat-units demanded of the coal to make the necessary- 
steam.. In an exhaust to the atmosphere, the heat rejected in the 
weight and temperature discharged is not returnable to the plant 
directly. 

5. The lowered temperature in the expansion at the end of the 
stroke causes the cylinder to reject less heat per stroke than in the 
non-condensing engine. 

The mechanical advantages are those of increased power due to 
lowered back-pressure, or increased area for the indicator card, and the 
smaller lighter engine cylinder resulting. The heated water produces 
less strain upon the plates or elements of the boiler, by lessening the 
stresses from unequal contraction under pressure (paragrafs 193 and 
132). 

The condensed water is pure distilled water free from chemical 
compounds. It is of advantage for use in boilers as it deposits no scale 
(paragrafs 185 to 189), and in marine practice the same pure water 
can be used over and over again without bringing into the boiler the 



EXPANSIVE WORKING OF STEAM . 463 

acids from the sea-water. This is also true for land conditions where 
good feed-water is expensive or not available. 

The physical principle on which the condensation of steam causes 
the practical vacuum is that one cubic inch of water will form 1658 
cubic inches of steam at the pressure of one atmosphere. If these 1658 
(often called 1700) cubic inches of steam are cooled back to water, they 
undergo a reduction of volume in the Game proportion less only the 
volume filled by the tenuous vapor which even cool water gives off in a 
vacuum. It will only be necessary to draw off the condensed steam as 
water by proper apparatus to enable the vacuum to be maintained 
which the condensation has created. 

The earliest historic steam-engines of the modern period were all 
condensing engines. Steam at a comparatively low pressure above 
the atmosphere was admitted to the cylinder for the working stroke, and 
upon being condensed the absence of pressure represented by the vacuum 
upon the working side of the piston was the principal dependence for 
the power of the stroke. Such engines were called low-pressure engines. 
When the engine did not condense, so that the back-pressure line in 
Fig. 418 was at atmospheric pressure or above it, it was necessary that 
the pressure of the steam in the boiler should be correspondingly raised. 
Such non-condensing engines were therefore run at relatively high 
pressure, and were called high-pressure engines. At one time, there- 
fore, high pr^sure was synonymous with non-condensing, and low 
pressure synonymous with condensing. This is no longer the case^ 
since nearly all condensing engines of modern constructi-on operata 
with steam at high pressure. 

307. Disadvantages of the Condensing Engine. The disadvantages 
of the condensing engine are also in two groups, the thermal and the 
mechanical. In the thermal class are: 

(1) The greater temperature range in the cylinder and the lowered 
final temperature increase the loss by thermal interchange of heat 
between the working steam and the metal of the cylinder walls; 
During exhaust the condenser temperature prevails, considerably 
below 212° Fahr., and greater initial condensation occurs, and re- 
evaporation loss (paragraf 300). 

(2) Condensation increases the heat flow and condensation in the 
steam-jackets of the cylinder, if these are used, both in the heads and 
around the barrel of the latter, causing a loss of heat which ultimately 
flows away with the cooling water. 

The mechanical losses are caused by: 

(3) The necessity for the cooling water for the condenser. This 
has to be paid for in taxes or in interest on the plant. In some places 



464 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

water is hard to get, as in climates where there is a long dry-season, 
or little rain-fall, or where there are no streams or bodies of water. It 
may be necessary to cool the injection water and use it over and over 
again. 

(4) The pumps and apparatus for handling this cooling or *' injection " 
water are costly, heavy and bulky, unless a natural flow is available: 
cooling apparatus if required is also costly and bulky. 

(5) The cost and maintenance of pumps and apparatus to maintain 
the vacuum in the condenser are an added expense to the engine, as 
well as the condenser, and the power to operate these and the injection 
pumps are elements of cost to be deducted from the gain from condensing. 

(6) If these pumps are operated by the engine itself, they limit 
its speed, or the engine speed limits theirs, according to circum- 
stances. 

(7) The condensed water from the condenser and in the hot- well 
carries with it the oil used in lubricating the cylinder piston valves 
and the like. The lubricating material must undergo the cooling of 
the condensing process, and gradually fouls and stops up the passages 
through which it passes, or else it goes through to be pumped back with 
the warmed water into the boiler. This presence of lubricating oil 
in boilers is a serious annoyance, inasmuch as a coating of suqh material 
on heating surfaces prevents intimate contact of water with the metal, 
and frequently causes the latter to become overheated and so softened 
as to be easily forced out of shape by the pressure in the boiler. Great 
care has to be taken to separate the oil from the condensed steam in 
the condensing engine to prevent this difficulty. See paragraf 246. 

The condensing engine can only be used where an available quantity 
of water for condensation can be procured without excessive cost. 
This limits the application of the principle to stationary pracftice on 
land, but is a reason for the abundant and extensive use of the con- 
densing engine for marine purposes. Condensation by air requires an 
enormous bulk for the condensing appliances, and where water is 
costly or scarce special provision must be made for using the same 
water over and over again. It is practically impossible to operate the 
locomotive as a condensing engine. 

If the heat in the exhaust steam can be used for heating air for 
buildings and shops or tanks or solutions in manufacturing, so as to 
release the steam-boilers from furnishing such steam in addition to that 
required for power, the condensation of exhaust steam is undesirable 
and unwise. In such cases the engine may be regarded as a form of 
reducing valve as respects pressure in such heating coils relatively to 
that in the boilers, so that in effect the manufacturer gets his power 



EXPANSIVE WORKING OF STEAM 465 

for nearly nothing if he can use all the heat in the exhaust steam for 
heating. 

The mechanical apparatus in the way of condensers, pumps and 
the methods of effecting condensation and maintenance of vacuum 
pressures and temperatures will form the topics of a later chapter, 
under engine-room auxiliaries. 

308. The Compound Engine. The condensation loss from the great 
temperature range of the condensing engine suggested the advisability 
of dividing the expansion process into stages, so as to distribute the 
heat interchange among two or more cylinders, in each of which the 
range should be less. This thermal concept brought with it so many 
mechanical advantages, and so wide a range of mechanisms to embody 
it, that its discussion will be taken up in the following chapter. 

309. The Computation of the Mean Pressure in Expansion. Reference 
was made in paragraf 301 to the naathematical procedure for computing a mean 
pressure of a gas expanding in volume. The methods of the calculus are the most 
convenient. 

When a fluid of volume v undergoes an infinitesimal increase in volume dv, while 
the pressure is assumed constant for that small increase in volume, the work done is 
pdv. If the fluid at v^ increases to V2 and the law of such expansion is pjVi = 
P2V2 = pv, the total work done within these limits will be 

J'"? /'V2 1 V 

pdv = pi^i ) - dv = p{Vi log — . 

But - = r, the ratio of expansion (Fig. 420) : and if there was work done before 

cut-off and expansion begin while pressure was coming in p^ and working through 
the space v^, this work was p^v-^ and should be added to the expansion work. If 
there is a back-pressure p^ acting constantly through the space v^, the total work 
will be the algebraic sum of the three, or 

Work = piVi + piVi log r — p^v^. 

But this work equal to the area under the line bounding the pressure ordinates 
will be equal to the product of a mean resistance or a mean pressure acting through 
the same length V2 ; hence the value for the mean pressure will be found by dividing 
the work by V2 ; or 

log r\ 



P"^=J = ^^^(^+^°^0"^^^^^(~ 



If there is no back-pressure, p^ disappears. 

If, on the other hand, the expansion is not at constant temperature, or isothermal, 
then the exponent for v will not be unity. Call it n. Then 

PlVi" = P2V2'', 

and 

pdv = PiVi"' \ v~^dv , 



463 MECHANICAL ENGINEERING OF STE.AJVI POWER PLANTS 

which can be transformed into 

and if admission work pit\ be added to it, and back-pressure work subtracted, 

so that the mean effective pressure becomes 

_ TF _ p, (n _ 1_\ 
^"^ v^ n-l[r /"y ^'' Fig. 420. 

In the steam cyhnder of — -: X L cubic feet, with a cut-off — the volume of 
144 r 




steam per stroke 



AL 

144 r 



The work done under the hypothesis first presented is 



pmAL per stroke. Hence the work done per cubic foot of steam is 
^ jj^ = 144 [pi (1 + log r) - p^r) 

When pi and p^ are assumed this is a maximum for r = — as discussed in para- 

graf 303. 

The work in terms of pressures instead of volumes above will take the form 

and in terms of absolute temperatures 



CHAPTER XVIII. 

THE COMPOUND AND MULTIPLE-EXPANSION ENGINE. 

315. Compound Engine defined. A compound engine is one in 
which the process of expanding the motor or pressure fluid from its 
initial high pressure to its final low pressure is done in two stages or in 
two steps in two or more cylinders. The reverse process is done in a 
compound compressor. The single cylinder of the previous types will 
be the same in the compound as in the simple, since the terminal pressure 
determines the final volume of the steam at the moment when the 
exhaust opens, and this final volume (called V2 in the computations and 
in Fig. 420) is the volume corresponding to the product LA in cubic 
feet in the formula for horsepower. The second cylinder or extra 
cylinder in the compound is the smaller of the two, introduced between 
the main or low-pressure cylinder and the high initial pressure from the 
boiler or reservoir of pressure. 

As the expansion line may go down below the line of atmospheric 
pressure, or may be cut by the line of back-pressure above the atmos- 
pheric pressure, there will be two types of compound engine. The 
condensing compound has the low-pressure cylinder condensing: the 
non-condensing compound, or the engine which is compound above the 
atmosphere, has no condensing cylinder, nor condensing apparatus. 
The small cylinder taking the higher pressures is always non-condensing, 
and is called the high-pressure -cylinder. Its exhaust is the initial or 
driving pressure for the low-pressure cylinder. 

In the normal or type compound, both cyHnders deliver their effort 
to a common engine shaft, either through one crank or through two or 
more. The compound engine has therefore thermal advantages due to 
the division of the expansion work on the diagram, and practical or 
mechanical advantages due to the use of more than one crank-pin and 
the distribution of effort of the expansion upon several cranks. These 
will be examined separately. 

A triple engine, or triple-expansion engine, is one which divides the 
work of the expansion process into three stages or steps, and uses three 
or more cylinders for the process. 

A quadruple-expansion engine is one which divides the work of the 
expansion process into four steps or stages, and uses four or more 

467 



468 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



cylinders for the process. There are no large installations higher than 
four stages, on account of the inconveniently high initial pressures 
required in the boiler to make them significant, and the cost of such 




Fig. 426. 

large engine. The usual range of selection of type with initial pressure 
will approximate: 

For a pressure below 80 lbs., use simple engine; 

For pressures between 80 and 120 lbs., " compound engine; 

'' 130 and 160 " " triple 



above 170 lbs., 



quadruple 



THE COMPOUND AND MULTIPLE-EXPANSION ENGINE 469 

If the two pistons of the compound engine are upon the same piston- 
rod as in the tandem or steeple types to be presently reviewed, the ratio 
of the work done in the two cylinders is not specially significant. A 
sound principle of proportioning would be to make the surface exposed 
to heat transfer in the two cylinders bear a ratio to the heat disposable 
in each, or to make the heat range equal in the two. Mr. George I. 
Rockwood has designed engines on this basis with a volume ratio of 
7 to 1. Ordinarily, however, the two cylinders have each its own 
crank; and here the distribution of equal work on each crank makes it 
a better arrangement to divide the work diagram. Figs. 425, 426, into 
two parts of equal area for the compound, and into three parts for the 
triple. This tends to keep the efforts of the cranks in balance. The 
two cylinders have nearly always the same stroke, so that if the mean 
pressures are to be assumed equal, the cylinder volumes must be related 
to these pressures. 

Let R denote the ratio between the volume v of the small cylinder and V the 
volume of the large. Let E be the total number of expansions: then if e be the 
ratio of the expansion in the small cylinder, E = eR. Assume the initial pressure 
Pi and the pressure at the beginning of the stroke of the larger cylinder to be p: 
then 

F 
Pi =^P =-^P' 

The two mean pressures will be determinable from the formula of paragraf 309, 
and the work to be equaHzed will be 

V 

-Pi (1 + hyp log e) — vp for the small cylinder, 

and 

V 

-^ p (1 + hyp log R) for the large cylinder, 

back pressure in the large being assumed zero for simplicity. Then reducing after 
equating: 

hyp. log £" = 1 + 2 hyp. log R, 

or 

hyp.logfi='2Pif^^. 

If the back-pressure be taken at 17 pounds and the initial pressure at 153 absolute, 

V 
the ratio of total expansion is 9, and R =— = 1.81. This explains and justifies 

the usual ratio of diameter of 1.8 to 2, when both pistons have the same stroke. 

Usual cyUnder-ratios of practice for usual pressures with triple engines 
are: 



470 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



Pressures. 



130 
140 
150 
160 
170 



Small. 



Intermediate. 



2.25 
2.40 
2.55 
2.70 



Quadruple engine preferred. 



Large. 



5 

5.85 
6.90 
7.25 



For quadruple-expansion engines the usual ratios of cylinder-areas 
and volumes approximate 1:2: 3.78 : 7.70, which may be called 
1:2:4:8. 

If the principle be adopted that the ratios of areas are to be as the 
fourth root of the number of expansions, the ratio of the first to the 
fourth will be as the cube of the fourth root. The ratio will increase as 
the initial pressure becomes greater; e.g., 1 : 2.2 : 4.8 : 10.6. 

The expansion in two stages need not be made in two cylinders only. 
The high-pressure cylinder having a volume, v, may deliver its steam 
into two larger cylinders of equal area whose aggregate volume is V. 
Such engine with three cyhnders, however, is only a two-stage expansion 
or compound engine. Similarly, the triple may have a high, an inter- 
mediate, and two low-pressure cylinders, or four in all, and yet be a 
three-stage expansion engine. The emphasis is upon the number of 
steps in the expansion of volume and not upon the number of cylinders. 

Again, the mechanisms discussed in paragraf 291 where cylinders 
were twinned, or set up double-opposed, in order to get piston area 
without excessive diameter for the cylinder, must be distinguished from 
the compound or triple-expansion engines of several oylinders. The 
essential point of difference is that twin or multiple-cylindered simple 
engines receive their supply of motor energy to all cylinders equally 
from a common source in engines of this class, while in the continued- 
expansion class, whatever the number of cylinders, the cylinders are in 
a series, of which some receive their motor energy after others have first 
withdrawn a part of such energy either in the form of heat or pressure 
or both. 

316. Thermal Advantages of the Compound Engine. The heat saving 
or thermal effectiveness of the compound and multiple-expansion 
engine referred to in paragraf 308 appears in four ways. 

1. The internal condensation loss in the cylinder is due to the tem- 
perature and pressure range with large expansion ratios. Steam cannot 
exist at T^ in a cylinder which has cooled to T^ during the last exhaust 
stroke. This cooling of the metal seems practically instantaneous, and 
no engine has ever run fast enough to outrun the condensation process. 



I 



THE COMPOUND AND MULTIPLE-EXPANSION ENGINE 471 

The incoming steam at T^ parts with some heat to warm the metal, and 
some steam is condensed in that cooling, to be reevaporated later, and 
at the lower pressure, getting necessary heat for such vaporization from 
walls and steam. Now the cooler the walls during the exhaust stroke, 
the more rapid and complete is the transfer and cooling, since the 
laboratory and experience show that such transfer is greater, the greater 
is the difference of the temperature of the two masses, one being cooled, 
the other being heated. If there could be no difference in temperature 
there would be no transfer and no condensation. The compound, by 
dividing the pressure range, divides the temperature range, and hence 
the loss in each cylinder or in both together is less than it would be in 
either if it were compelled to pass through the entire temperature range 
of the desired expansion. 

2. Any steam condensed in the simple engine cylinder and not 
evaporated until after the exhaust opens, evaporates without doing 
work, and both heat and pressure effect are lost. In the compound, 
such condensation in the high-pressure cylinder, whether due to initial 
cooling or cooling during an adiabatic expansion, does work in the low, 
and is sure to be evaporated under the lower tensions of the big cylinder, 
and not escape as water. 

3. The high-pressure cylinder of smaller volume than the low loses 
less heat from the hot steam by external radiation than if such hot 
steam were received into the large low-pressure cylinder directly. 

4. The mechanical possibilities of the compound enable it to work 
at higher initial pressures than the simple engine when the back-pressure 
is fixed, and thus reap the full advantages of expansive working. To 
increase the pressures in the boilers is to carry more stored energy in a 
given space; to use higher pressures is to enable each cubic foot or pound 
of steam to carry more energy into the engine-cylinder, and a given 
quantity of heat raises the pressure of steam more rapidly after the 
steam has become a complete gas than it does at lower pressures, when 
a large part of the heat is absorbed in changing the molecular condition 
of the water. 

317. Mechanical and Practical Advantages of the Compound Engine. 
The principle of expanding in two or more stages may be applied in 
many differing arrangements of the necessary mechanism. Mechanical 
advantages of the type will therefore apply in differing degree to such 
varying forms, and differing adjustments. Among these advantages 
are : 

1. The high-pressure steam comes upon a piston area at admission 
from the boiler which is less than in the simple engine of same power. 
There is less stress on rods and pins and on the piston itself. 



472 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

2. The clearance volume of the small high-pressure cylinder carries 
less steam by weight than if steam at that pressure had to fill the same 
length of the large low-pressure cylinder as in the simple type. 

Such clearance steam in the high expands into the low and does work 
instead of going out with the exhaust. 

3. Leakage past valves and pistons is less with the smaller masses 
of the high-pressure engine. Such leakage again is used to do work in 
the low. The higher the pressures the more leakage through a given 
opening in a given time. High heat of steam increases likelihood of 
such leakage. 

4. The equations (paragraf 315) for total expansion E = Re, where 

V 

R is the ratio of the volumes — , lead to an interesting and valuable 

V 

feature of the compound. If there is no cut-off whatever in the high- 
pressure cylinder, and the steam at boiler pressure follows the piston 

V 

full stroke, so that e = 1, the total expansion E is equal to R = —. 

V 

That is, by the compound principle expansion is secured while the steam 
follows full stroke in the small cylinder: or, the advantages of expansive 
working are secured without the disadvantages of an early cut-off in a 
single cylinder. If the back-pressure be fixed and the final volume V2, 
then the value of the second member of the equation 

becomes fixed. The initial pressure p^ is also usually fixed by the 
convenient boiler pressure; but for reasons hitherto advanced it should 
be as great as consistent with safety and convenience. Hence the 
value of v^ must be 

v, = - — ^ 

Pi 

giving a small value for v^. If this is a small fraction of the length of 
the stroke V2 of a single or simple engine the high pressure jo^ comes on 
the piston during such a part only of the crank-motion that it is not 
effective to produce rotation, but the effort goes into the component 
velocity along the crank itself (paragraf 261) causing bearing friction 
rather than rotation. In the compound, however, the same expansion 
is secured and the high pressure exerted through the best crank-angles. 
This is an argument for the compound system with air and non-con- 
densible gases where the thermal arguments are without significance. 

5. This makes the compound waste less applied effort in bearing 
friction in spite of the increased number of rubbing surfaces. The 



THE COMPOUND AND MULTIPLE-EXPANSION ENGINE 473 

heav}'' pressure is upon smaller piston areas; and conversely, the large 
areas have only the reduced pressures upon them after some expansion 
has occurred. 

6. The prolonged time for admission of steam through valves and 
ports to the high-pressure cylinder, as compared to the short period for 
opening into a simple cylinder to get the same expansion, enables full 
pressure to be realized in that first cylinder of the compound. The 
openings would have to be closed so soon in the stroke of a simple 
engine that the steam would be wire-drawn, or else ports and passages 
used of such size as to make excessive clearance loss. 

Certain compound engine mechanisms derive advantages in addition 
to the above which are peculiar to them. If the cyhnders deliver their 
effort to the crank-shaft each through its own crank-pin: 

7. Such engines avoid the concentration for large engines of great 
energy on small areas, and enable designers to avoid either excessive 
lengths or inconvenient diameters for their crank-pins. When the 
crank-pin becomes of inconvenient diameter with respect to the length 
of the crank, the angle during which the pressure of steam is available 
to produce rotation of the crank is diminished. 

8. The turning effort is equalized when the compound engine is 
arranged to have its cranks quartering. The distribution of recipro- 
cating weight over two crank-pins in vertical engines makes balance 
around the shaft more easy to secure (see Figs. 439, 440). This 
diminishes the weight of the fly-wheel and the amount or intensity of 
vibration of the bed-plates. 

9. The compound engine gives an opportunity to improve the quality 
of the steam during the process of expansion when it is possible to use 
a reheater such as shown in Fig. 393. 

318. Disadvantages of the Compound Engine. These are also in 
two groups. The thermal objections are: 

1. The loss of available work or diagram area in free expansion of 
steam into the passages from one cylinder to another; also friction of the 
fluid in such passages and condensation therein. These losses show 
when diagrams of a continuous action of a given mass of steam are 
superposed to scale as in Fig. 426. and are not incurred in the simple 
engine. 

2. The free expansion or unused energy of the steam expanding in 
clearances of cylinders after the first. 

3. The losses from radiation of heat from surfaces of the additional 
cylinder and valve-chest. 

The objections from the mechanical or practical point of view are: 

4. The cost of the cyhnders other than the low. In tandem engines 



474 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

this may mean the cost of piston and cylinder with additional rod, but 
in cross-compound and fore-and-aft engines it means an additional 
cost of practically another engine with crank, connecting-rod, cross- 
head, and the hke. 

5. The weight and bulk of the additional cylinder adding to founda- 
tions and taking up valuable space. 

6. The repairs and maintenance and up-keep on such additional parts 
as are added to the typical simple engine to make it compound. 

7. The friction-loss due to the work absorbed by this extra cylinder 
in operating its mechanism, valve, and the like. 

8. The difficulty connected with regulating the power of the engine 
when the work varies widely, and the first cylinder has measured off a 
volume of steam adapted to a resistance different from that upon the 
engine when that volume of steam reaches the later cylinders. This is 
the difficulty of governing the multiple-expansion engine, except by 
regulating devices operating upon each cylinder independently. 

9. The limitation of power-output because the compulsory expansion 
makes it impossible to get a larger value for the mean-pressure in an 
emergency than was intended by the designer. This has been an 
objection in railway service with two-cylinder compounds, that they 
did not allow of making up time in storms or delays by making a very 
late cut-off to get power. The end can "be served by fitting a by-pass 
or small pipe connection from the boiler-pressure pipe to the low- 
pressure cylinder, and " bleeding " live steam into the low-pressure 
cylinder through a controlling valve. Since such bled steam to drive 
the low-pressure piston is necessarily a back-pressure against the high- 
pressure piston, the engine as a whole benefits only from the fact that 

V 

the low-pressure piston is larger than the high by a ratio — • If full 

boiler pressure is admitted to the low-pressure cylinder the high- 
pressure piston passes into equilibrium of pressures on both sides of it 
and goes out of effective action. 

10. The high grade of expansion makes it impossible to start the 
engine from rest if the high-pressure cylinder is on a dead-center or 
there is no steam getting past that piston to the low-pressure engine. 
This is met by an " intercepting- valve," a by-pass admitting steam to 
the low-pressure cylinder directly from the boiler, and by the availability 
of this large area a powerful starting moment or torque is also secured. 
The intercepting valve may cause the high-pressure cylinder to exhaust 
to the open air or to the condenser while it is open, and thus put both 
cylinders in action for a few revolutions. The intercepting valve may 
remain under the control of the human intelligence starting the engine, 



i 



THE COMPOUND AND MULTIPLE-EXPANSION ENGINE 475 

or the engine may automatically close it and become automatically 
compound when a certain pressure is reached in the connection between 
the two cylinders. Such compound engine starts like two simple 
engines, and the valve is sometimes called a simpling valve, and the 
operation simpling the engine. It can be used to meet objection 
Xo. 9. 

11. There has been considerable trouble in compound engines from 
the accumulation of water in the low-pressure cylinders, particularly 
when compounding above the atmosphere and using wet steam. The 
wide range of expansion, the lowered terminal pressure, and the large 
diameter of the low-pressure cylinder have made this difficulty a very 
troublesome one in locomotive practice. 

It is obvious that the weight to be attached to the above objections 
is not considered by most designers to be great enough to overbalance 
the advantages which follow from the principle of compounding. 

319. Mechanisms of the Compound Engine. The engine mechanism 
which is to carry out expansion on the compound principle will embody 
one of two systems. The one system will he that in which the two 
pistons will have their motion controlled l)y a crank or cranks which 
compel them to be at all times in the same phase of their motion and to 
pass their dead points and begin and end their stroke and to pass their 
90° and 270° points of crank motion together. The pistons at the dead- 
centers may have completed a traverse in the same or in opposite 
directions. The other system has the two pistons acting upon cranks 
which are not in phase, but may be 90° apart or quartering, or 120° 
apart in the triple engine or three-cylinder compound. 

In the first S3'stem, the mechanism appears in three general forms: 

1. Both pistons on the same rod, tandem, with one piston-rod, one 
cross-head, one connecting-rod, and one crank. 

2. The two pistons each on its own rod, driving a common cross- 
head or a common beam with one connecting-rod and one crank from 
that common cross-head or beam. 

3. The two pistons each with a complete engine mechanism operating 
upon its own crank. The cranks may be at 180° apart, or (very rarely) 
parallel. 

The type with the two pistons moving in the same direction together 
is the simplest form, proposed by Arthur Woolf in 1804 and often called 
the Woolf type. 

The other class compels the use of a receiver between the two cyhnders 
to receive nearly the half contents of the high-pressure cylinder. If 
the cranks are 90° apart the low-pressure cylinder will be at its dead- 
center when the high -pressure piston has still a half stroke to make 



476 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




COMPOUND AND MULTIPLE-EXPANSION ENGINE 



477- 




FiG. 431. 



47S MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

before it comes to rest. Hence the exhaust of that high-pressure 
cyhnder must be received in an adequate receiver from which it can 
pass to the low when the latter is ready for it. 

330. The Tandem Engine. The Steeple Engine. Beam Compounds. 

When the two pistons are on the same rod in a horizontal engine, it 
will be called a tandem-compound (Figs. 430, 505). When this same 
engine is. preferred with vertical cylinders it is a steenle or cupola engine 
(Fig. 431). 

The feature of the tandem engine is the lowered cost of the type, since 
the extra cylinder piston and valve with its mechanism are the only 
parts added to the simple. In the form shown in Fig. 430 a long internal 
sleeve forms the stuffing-box between cylinders, but it is inaccessible 
without taking the engine down. In Fig. 430 the cylinders are separated 
to give access to the two stuffing-boxes now required, and the engine is 
longer. The steeple compound will rarely be used except in short 
stroke marine engines because of its inconvenient length. Figs. 430, 
431 and 505 show the more usual arrangement with the heavy low- 
pressure cylinder close to the massive part of the bed plate, and giving 
the lighter high pressure its support from the low. This is not impera- 
tive, and Figs. 433 and 434 show this reversed. The larger diameter 
of the low permits the valve rod to pass by the high. Fig. 434 is of 
interest from the presence of a reheater between the steam cylinders, 
and a device to give out work at the end of expansion instead of a fly- 
wheel for that purpose. Plungers which swing upon trunnions are 
forced forward by pressure from the water main at the end of each 
stroke and help complete the piston traverse under the fall of pressure 
toward the end of the diagram of work. The objection to the tandem 
is that the steam from the high-pressure cyhnder has to travel the 
length of the low cylinder outside of its bore to supply the end furthest 
from the high. 

The beam types of mechanism were early utilized by the designers 
of compounds. The first Hornblower type of 1781 was a beam engine, 
and his general design of two cylinders side by side acting upon a 
beam has been widely adapted for water-works pumps. Early simple 
beam engines compounded by the addition of a high-pressure cylinder 
were said to be " McNaughted " from the name of the designer who 
first proposed it (Fig. 435). Or, the two cyhnders may take hold on 
opposite ends of the beam, as in Fig. 391, in which case the two pistons 
work in phases 180° apart, and very short steam passages are required 
between the two cylinders. Figs. 393 and 394 show the two pistons 
connected to opposite ends of the beam, the arrangement used in the 
great sewage pumping-engines of Boston, Mass., with the beam below 



THE COMPOUND AND MULTIPLE-EXPANSION ENGINE 479 




480 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




THE COMPOUND AND MULTIPLE-EXPANSION ENGINE 4S1 








482 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

the cylinders, and Fig. 392 is a most compact and short-passaged design 
with the beam length vertical. 

The only important example of two paj^allel cylinders side by side 
with two separate rods to a common cross-head is in the Vauclain or 
Baldwin compound locomotive. The difficulty is the varying effort 




Fig. 435. 



upon the two rods except when the conditions of pressure assumed in 
proportioning the respective areas happen to be met. The valve can 
be placed between the two cylinders and a simple gear only is required. 



THE COMPOUND AND MULTIPLE-EXPANSION ENGINE 



483 



The cross-head requires to be very long to prevent " cocking " when 
starting, and water in the low-pressure cylinder produces a strain out 
of the axis of the thrust of the connecting-rod and is apt to crack the 
cross-head. 

331. The Fore-and-Aft or Side-by-Side Compounds. The advan- 




FiG. 436. 



tage of getting the work from the pistons to the engine shaft through 
two crank-pins has given wide acceptance to this type either with the 
pistons moving together or in opposite phase with cranks at 180° 



484 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

apart. The latter is the only one in American use, because the weights 
of the two mechanisms are in balance on opposite sides of the shaft in 
vertical engines, and this type is practically restricted to such engines. 
In marine engines the cylinders were one behind the other over the 
shaft, or fore-and-aft. Fig. 436 shows the side-by-side inverted vertical 
type and a small detail of the high-pressure valve, and Fig. 437 a 
developed section of another similar type. These show also what is 
called the piston- valve. In shallow hulls for Hght-draft vessels this 




Fig. 437. 



arrangement gave less vibration from unbalanced or unequal effort on 
the up and down strokes and lessened the stresses on the bearing between 
the cranks. The passages are short as in the beam arrangements for 
opposite phase of the crank. Figs. 403 to 405 show single-acting com- 
pounds of this type. 

323. The Cross-Compound Engine. Receiver Engine. The cross- 
compound engine is the exemplar of the third group when the cranks 
are quartering or 90 degrees apart. It may be defined as a com- 
pound engine with parallel cylinders side by side and cranks at 90° 
apart : the space between the cylinders being large enough to take in 
a pipe or chamber to act as a receiver of the exhaust-steam from the 
high at such times as there is no low-pressure cylinder- volume to receive 
it. This happens at and near the dead-centers of the low, at which 



THE COMPOUND AND MULTIPLE-EXPANSION ENGINE 485 

time the high-piston is moving at its most rapid rate, sweeping the 
exhaust out from the previous stroke. Cross-compounds quite usually 
have a cut-off valve action in the low-pressure as well as the high, for 
which there has been no room nor call in the previous types. 

Cross-compounds are either horizontal (Figs. 438, 504) or vertical 
(Fig. 380). It is very usual to put the fly-wheel or generator between 
the two cranks. It is not clear whether it gets its name from being a 
cross between the two previous crank arrangements, or because the 
steam crosses over the space between the two cylinders (Fig. 438). 
The quartering cranks give more equable turning moment, do not 
compel all the reciprocating masses to be accelerated at once or in one 
quadrant, and lessen the fly-wheel weight. The horizontal vertical 
engine when compound (Fig. 387), as it usually is, reaps these advan- 
tages. The inclined engines of Figs. 384 to 386 and 503 are also cross- 
compound mechanisms. 

323. The Triple-Expansion and Quadruple-Expansion Engine. In 
the triple-expansion engine, the cranks are usually at 120° apart to 
equalize turning effort and the acceleration influences. These mechan- 
isms are horizontal or vertical, or show the combined horizontal and 
vertical. The marine use of the triple engine has given a vogue to 
the inverted vertical type (Fig. 381) and the multiple pistons on oppos- 
ing cranks enable balance to be aimed at by making the small piston 
and attached weights more massive than needed for strength. But 
there will be a period in each revolution when two of the pistons will be 
descending and only one ascending, and this inequality must be provided 
for. Moreover, the crank-shaft wdth multiple cranks is a costly and 
troublesome proposition, so that even with quadruple expansion, for 
economy of room and to shorten the crank-shaft only three cranks will 
be preferred. Figs. 439 and 440 show arrangements which have been 
used to overcome these difficulties. 

324. The Compound Locomotive. The locomotive is a compound 
above the atmosphere, and its fuel economy diminishes the weight 
for the tender in a given run. It is at its best in long steady runs with 
infrequent stoppages and at efforts near the maximum. Frequent 
stops and starts either in marine or locomotive conditions put the 
compound under its worst disadvantages, and the heavy draft for power 
in accelerating trains after stops is best met by the simple engine. 

The mechanical arrangement appears in several differing types. 
First the two-cylinder compound, which is a cross-compound, v/ith a 
reheating action in the cross-over pipe in the smoke-box. Usually the 
high pressure is on the left side and the low pressure on the right. 
The diameter of the low is limited by lack of room laterally. The 



486 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




THE COMPOUND AND MULTIPLE-EXPANSION ENGINE 487 




f D I 



Fig. 439. 



488 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



/ 



T 



MJP. 



^■ 



t 



HP. 

.1 



MlP. 
3 



_t5_ 



L.P. 

4l 




MlP. 

2i 



lIp. 

4l 



HiP. 

ll 



MJP. 
3i 



MlP. 

2i 



MlP. 



L.P. 

4 



M.P. 
3 



LiP. 

4i 



H.P 

li 



MP. 
2 



O ' p 

Fig. 440. — Grouping of Cylinders in Quadruple-Expansion Engines. 



THE COMPOUND AND MULTIPLE-EXPANSION ENGINE 489 

intercepting or starting valve will be either automatic, starting the 
engine simple, and changing over as pressure accumulates in the 
receiver; or it will be under the control of the engine-man; or the opera- 
tion of the cut-off lever in increasing the rate of expansion after the 
starting inertia has been overcome will compound the engine. The 
successful steam motor vehicles are two-cylinder compounds, with the 
intercepting or starting-valve under the control of the operator. 

The second arrangement has three cylinders. This is a more preva- 
lent European design, and is not used in America. Usually the two 
cylinders which form the low-pressure stage are outside the frames in 
the position of the usual outside-connected engine, and the high-pressure 
cylinder is between the frames under the smoke-box. This central 
cylinder drives the forward driving-wheels by means of a cranked axle, 
and the outside cylinders drive the rear or trailing wheels by outside 
crank-pins. This arrangement is also sometimes reversed. 

The third arrangement is the four-cylinder compound, in which the 
high and low-pressure cylinders are attached in pairs on each side of 
the engine, in the common cylinder location, to a common cross-head, 
from which the usual driving-rod passes to the crank-pins and wheels. 
The advantage of this is that the engine works compound just like a 
simple engine and with the same valve mechanism, except that a 
simpling valve is required so that boiler steam may be let into the larger 
cylinder through a by-pass for starting. By using a pipe of small 
cross-section for such by-pass connection, the pressure on the areas of 
the two pistons is not allowed to be so different as to cause undue stresses 
in the cross-head. The high-pressure cylinder is either above or below 
the larger one, and both move together in the same direction. Hence 
the construction of the valve must be such as to pass the steam diago- 
nally from one end of the high-pressure cylinder to the other end of the 
low. This type requires no receiver and permits no reheater. 

In the fourth type the two cylinders are tandem on each side, on a 
common piston-rod on each side. This type avoids cross-strains on the 
cross-head, and valve-gear and starting devices are the same as in the 
preceding. 

The fifth type has four cylinders side by side, a compound engine on 
each side of the locomotive, and with the four cranks 90° apart in one 
of two systems. In both the high-pressure pistons drive a cranked 
axle on the forward or main drivers, the two cylinders being between 
the frames, while the low-pressure cylinders are outside the frames, and 
their pistons drive the rear or trailing drivers by the usual outside- 
connected mechanism. The pairs of drivers are coupled with side- 
rods externally. In one system the two cranks of each side of the 



490 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

locomotive are 180° apart, and this pair of cranks 90° from the other 
pair. In the other system each side has its cranks 90° apart, the two 
highs and the two lows being each 180° from the other. This latter 
makes a better balance in running. The advantages of the compound 
locomotive beyond those which it enjoys in common with any compound 
engine are the result of the lower terminal pressure at which the exhaust 
escapes. This is favorable to economy in the fire-box, because the fire 
is less torn by the pulsation of the exhaust, which causes the draft, 
and in cities the diminished noise of the escaping exhaust makes the 
locomotive less of a nuisance and the cinders are less thrown. The 
increased number of parts, with increased cost and time for repairs to 
them, and the inaccessibility of parts placed under the boiler, have 
prevented the rapid or wide introduction of the compound except for 
continuous through runs of heavy trains. Compounds do not make 
up time easily after road delays. 

335. Compounding above the Atmosphere. The general discussion 
of Chapter XVII, which showed that the greater the back-pressure the 
less the advantage from expansion, should have made it obvious that 
the compound system as a means to secure and favor expansion is not 
at its best in non-condensing engines. With a given initial pressure 
or the less the total area for the work diagram the more significant are 
the losses due to the compound, due to such back-pressure value. 
The distribution of work effect is present still as an advantage, and in 
pumping and similar cases the following of the full pressure through the 
stroke of the small cylinder is a mechanical advantage. Where the 
exhaust-steam is to be used for heating, and requires heat and pressure 
to be valuable for this purpose, the divided expansion may still be 
advisable for this reason, while without significance in heat economy. 

With compressed air motors, as for street railway service, where the 
demand that great store of energy be carried in pressure tanks of small 
bulk and hence under high tension, and where the exhaust tension 
must be that of the atmosphere to prevent noise upon the streets, the 
compounding of the engine is desirable for mechanical reasons. There 
is no heat gain from the process, except that from distributing an incon- 
venient temperature drop in the expansion process; but in starting and 
in equalizing stresses over piston areas the system has proved itself 
worth while. 

336. The Receiver and the Reheater. A rule of very general accept- 
ance is that the pressure in the receiver should not rise to nor exceed 
one-half that in the boiler or on the forward driving side of the high- 
pressure cylinder. In the cross-compound, the most unfavorable case 
would be met when there was no cut-off or expansion in the high- 



<t.^ 




492 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



? 


j 


-N 


" 111 .' 1 , . 


35 

■15 





V ; 


_i__4====4======F^^^^*^^^^^^^ : 




J 


C j 1 1 ' ■ i ' l t J 


15 









Fig. 442. 



pressure cylinder: one-half the volume of the high-pressure cylinder 
would therefore have to be provided for at boiler pressure, before the 
valve to the low pressure opened to receive steam. The limit of pressure 
would therefore be never reached if the receiver volume was equal to 
that of the high-pressure cylinder. 
The ratio varies between 1 and 1.5. 
In triples it can be less; and in 
most designs the valve chamber of 
the low-pressure cylinder, or the pipe 
connecting the cylinders, gives all 
necessary volume without inconven- 
ient fluctuations of pressure for the 
low cylinder, or undue drop or free 
expansion from the high. 

Fig. 441 shows a receiver design fitted to take the heating tubes to 
make such a receiver into a reheater or regenerator to improve the heat 

quality and dryness of the 
steam in transit from one 
cylinder to another. These 
heating tubes are supplied 
with hot dry steam from 
the boiler, always at higher 
temperature than the used 
steam which surrounds 
them. The reheating tends 
to close up the gaps in the 
combined indicator dia- 
gram. Figs. 387, 393, 434 
make obvious the use and 
construction of such re- 
heaters, which are a means 
of adding distinct economy. Reheaters require to be drained of 
condensation, and of course there is also condensation in the heating 
coils (paragrafs 243, 250). 

327. The Work and Indicator Diagram of a Compound Engine. The 
discussion of types of compound engine in paragraf 319 and those 
which follow shows that the expansion process of a given volume of 
steam will give rise to two differing types of indicator diagram for such 
combined cylinders. In the one type shown in Fig. 442, taken from a 
slow-speed low-pressure compound with little or no compression in 
either cylinder, the diagram of pressures upon the low-pressure cylinder 
should have its upper line the complement of the lower line of the high- 




FiG. 443. 



THE COMPOUND AND MULTIPLE-EXPANSION ENGINE 



493 



pressure diagram, because the larger piston is being driven by the steam 
which escapes from the smaller cylinder. Any discrepancy or lack of 
harmony between these lines in a Woolf engine without receiver indicates 
losses from friction, condensation, or unnecessary expansion in the 




Fig. 444. 



clearances or passages between the two cyUnders. In the receiver 
engine the steam in that receiver is to be treated as a steam spring 
receiving and storing work from the high-pressure cylinder and giving 
it out unaltered to the succeeding stroke of the low-pressure cylinder. 




Fig. 445. 



Any discrepancy between the hues of the two diagrams for the two 
cylinders indicates a drop caused by free expansion from the high- 
pressure cyhnder into the receiver without doing work in driving the 
low-pressure piston, as well as the losses from friction and condensation 



494 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

present in the other type. Such loss by free expansion is not usually 
recovered, and should be guarded against if the conditions of operating 
the engine permit it. 

For higher speeds, when accelerations are to be provided for by 
compression, the combined diagram takes the form of Fig. 443. Ex- 
haust from the high ceases at d and compression begins, accompanied 
by a gradual drop of pressure in the low, and loss of indicated work, 
but not necessarily of crank-pin work, since the masses of the fast 
moving parts are giving stored energy upon the pins. 

When the engine is of the receiver type, on the other hand, the volume 
of the latter may permit the back-pressure line of the high-pressure 
card to be practically horizontal, and the cards will be like Fig. 444 
when separate, and result in a Fig. 445 when superposed upon the 
same pressure scale. There are then two procedures possible. One 
is to get the area of each card and its M.E.P. by usual methods, then 




before adding them together to multiply the M.E.P. of the high-pressure 

V 

card by the ratio — of the twa cylinders to reduce the card of equal 

length to the same work scale as that of the low-pressure card. Then 
add the two together for the total mean pressure considered as exerted 
over the large diameter or last cylinder to get the horsepower. The 
other plan is to superpose the two cards on a common vertical scale, 
and related each to a proper allowance for their respective clearances. 
Then with a proportional dividers or other measuring device, reduce the 
horizontal measurements of the high-pressure card at several points of 

V 

pressure by the ratio — and draw the resultant expansion curve 

through the points thus determined. Thus, if the ratio of the cylinders 
is as 1 is to 4 let cd on the right hand of Fig. 446 be laid off one-fourth 
of the actual measurement of the card, which is CD in the original dia- 



THE COMPOUND AND MULTIPLE-EXPANSION ENGINE 495 

gram. It will thus appear that the reduced diagram will now represent 
on the same s^ale as the low-pressure diagram the work delivered upon 
its crank-pin, and we therefore have the net indicated work done in 
the, two cylinders presented by the combined diagram shown in Fig. 
446 at the right hand. This indicates to the eye the continuity of the 
expansion in a compound engine, and shows the space for loss between 
the two cylinders which would not be present if the expansion were in 
one cylinder only. It is this area which designers of continued-expan- 
sion engines are to reduce, and it is in spite of this loss that the 
compound engine is superior to the simple. Care must be taken in 
combining the diagrams of effort of steam in the two cylinders to put 
them in their right relation to each other vertically. This is accom- 
plished by means of properly relating each to the line of zero volume 
or of no clearance as appears in Figs. 425, 426. 

To find the steam in horsepower per hour from such a card, it will 
be apparent that if 

S denotes the weight of steam per horsepower per hour, 
w denotes the weight per cubic foot of steam at the mean pressure 
from the card, 

V denotes the per cent of volume of the cylinder or piston displace- 
ment filled hourly with steam when the pressure corresponding to 
w was measured or computed, 

Then 

M.E.P. X S = 19,800 XwXv. 

The value for v may be taken from either card, and its correspond- 
ing pressure. The two values from the two cards will usually differ 
slightly in an actual case from changes of load or governor action. 
The mean may be safely taken. The M.E.P., given in pounds per 

V 

square foot, should be multiplied or divided hy R = — -to correct for 

the volumes of the two cylinders and reduce to a common standard. 
This is the steam weight without condensation loss, or allowances for 
leakage, or for the quality of the steam.* 
* The derivation of this formula is: 

1 H.P. per hour = 33,000 X 60 = P^ X LA X iV X 60 

= P V 

But only — is filled at P^, and S = r^ 

Hence Pm^ = 19,800 xwxv 



496 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

338. Concluding Comment. It has been the effort and purpose of the 

preceding paragrafs and chapters to develop from the simple typical 
reciprocating steam-engine those forms and arrangements of it which 
have sought superior economy and efficiency, and particularly in the 
larger units. 

It is now desirable to return to the fundamental classification of para- 
graf 254 of Chapter XV and examine the engines of the second 
group. These are engines of the pressure class, but in a continuous 
rotary group having no reciprocating masses in the mechanism. These 
are called rotary steam-engines and will form the topic of the next 
chapter. 



CHAPTER XIX. 

THE ROTARY STEAM-ENGINE. 

330. Rotary Steam-engine defined. A rotary steam-engine is one 
in which the piston which receives the driving-pressure of the steam 
does not travel in a straight Hne along the axis of the cylinder, 
but revolves in a plane at right angles to such axis. Such piston 
or pistons — there are usually several in the cylinder — form or are 
attached to the crank-arm by which the engine shaft is revolved so 
that their rotary motion around the cylinder axis revolves the crank 
directly. The rod which was formerly the piston-rod of the recipro- 
cating engine and passed steam-tight through a stuffing-box in the 
cylinder-head is now the revolving shaft of the engine: the center of 
pressure of the driving fluid on the piston area is the center of the 
crank-pin. Piston-rod, cross-head, and connecting-rod, with their mass 
and inertia, have disappeared, and with them their cost of construc- 
tion, their joints to be maintained, and their lubrication. The power 
is applied directly to produce rotation. 

The piston will no longer be of circular section but probably rec- 
tangular. It must fit steam-tight to the surfaces over which it sweeps, 
and by reason of unequal expansions it cannot be fitted without pack- 
ing strips. It must be emphasized that the rotary engine is a pressure- 
utilizing motor, to distinguish it from the steam-turbine, which it 
outwardly or superficially resembles. The area to be used in the 
horsepower formula is the mean or average net effective area of any 
one of the pistons exposed to the forward action of the steam during 
that period when pressure from the pipe is acting on it. As soon as 
a second piston comes into action, the first one is no longer effective, 
but has the same pressure behind it as it has in front. The piston- 
speed is the path of the effective center of pressure of such a piston in 
one revolution multiplied by the number of revolutions per minute. 
By taking one piston area through a complete revolution, the necessity 
is avoided of finding out during what fraction of a revolution each 
piston is effective, and multiplying by the number of pistons. Each 

of n pistons is assumed to be effective during — th of the travel of 

n 

one revolution. 

497 



498 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

351. Types of Rotary Engine Mechanism. An inspection of Fig. 450 
presenting the basal concept of a rotary steam-engine will make clear 
the difficulty which its apparent simplicity has introduced. Such a 
mechanism as Fig. 450 would not turn over, because the pressure from 
the inlet / to produce intended clockwise rotation upon piston a is 
equated by an equal pressure upon c to rotate contra-clockwise. The 
steam between pistons a and b is inert, having equal pressures forward 
and backward over equal areas; while piston 6 has on one side the 
pressure prevailing when this space was connected to / and on the other 
the exhaust-pressure. Hence the net effect would be to drive c contra- 
clockwise, or on the wrong direction, if the pressure in E is lower than 
in/. 

If, however, the pistons were in the angular relation of Fig. 451 due 
to a partial rotation and the eccentric ring of that figure were absent, 
the pistons h and c are in equilibrium of pressures, but worse than 





Fig. 450. 



Fig. 451. 



this, a passage has been opened directly between inlet / and exhaust Ey 
and steam blows through to waste and does no driving of the engine. 
Hence a scheme must be found to accomplish the double purpose of 
separating the exhaust and inlet pressures at all positions of the pistons ; 
and to compel continuous motion of the pistons through the longer arc 
between the points of inlet and exhaust. This device is called an 
abutment, and takes many forms. Rotary engines are mainly differen- 
tiated from each other by the form of their abutment. In Fig. 451 the 
abutment is a revolving ring or cylinder, with its center of figure eccen- 
tric to that of the path of the pistons. The pistons fit the ring steam- 
tight with a rolling or rocking joint, and the ring fits both faces or 
heads of the cylinder closely enough to scop leakage across around its 
ends. The pistons in passing the point / retreat within the ring surface, 
but protrude on passing the contact point, and receive the pressure as 
at c in Fig. 451. As here shown, in the desire to get a considerable 



THE ROTARY STEAM-ENGINE 



499 



path for the piston under pressure, the area exposed, or the value of 
the turning moment, is small. If the inlet is lowered as in the dotted 
hnes at /^ the ineffective arc or length of piston action is decreased but 





Fig. 452. 



Fig. 453. 



the effective area is increased unless, again, in an effort to diminish 
clearance loss behind c in the position shown, a pressure is acting 
negatively on it to turn the shaft the other way. 




Fig. 454. 



Suppose now as in Fig. 452 the abutment ring is made solid, and 
instead of three pistons, they become four in an effort to lessen the 
volume of steam filling wastefully the clearance space between pistons 



500 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



a and d. The pistons can be forced out to their 
away with packing strips on the end faces, but 
pressure trouble appears unless the piston can 
abutment, or such negative pressure on d be 
sketch, with attendant excessive clearance. 

In the forms of Fig. 451 and 452 the center of 
the travel of the piston tips. It may therefore 



work by springs, doing 
the back or negative- 
be kept hidden in the 
neutralized as in the 

the abutment is within 
be called hypocentric. 



THE ENGINE. 




Fig. 455. 



In Figs. 453 and 454 are shown two types in which the abutment is 
outside the piston paths, or its center is epi-centric. The design of 
Fig. 453 is in effect what is called in kinematics a chamber-wheel gear 
with a diametral ratio of 1 to 3. If the diametral ratio be 1 to 2 the 
form becomes that of Fig. 454. The curves of closure are epi- and 



THE ROTARY STEAM-ENGINE 



501 



hypocycloidal with the curves traced by a common describing circle. 
The other type is kinematically a turning-block slider-crank chain. 

If now the abutment organ turning with the crank in the epi-centric 
class be made so as to have the same diametral ratio, or that of 1 to 1, 
the form of Fig. 455 results in which the two organs function alter- 
nately as piston and abutment. The pressure inlet is at A in these 
two latter figures. The unbalanced pressure upon the piston or crank- 
organ compels rotation of the shaft, and the two shafts of the piston 
and abutment element are kept in phase by gears outside the casing. 

If the rotary engine is not to be reversed, it requires only a throttling 
valve upon the pipe connected to the inlet /. If it be desired to reverse 
it on occasions, the form of Fig. 456 shows the simplicity of the required 

valve-and-seat construction. 
The sliding valve when thrown 
to the left by the rack and 
pinion geared to an external 
lever, compels a clockwise 
rotation. To reverse the slide 
valve is moved to the right; 
and in mid-gear, with both 
inlet and outlet covered 
motion stops. To pack the 
sli ding-contact surfaces, in 
most cases packing strips are 
provided which are forced 
outwards by springs acting 
radially. The shape of the 
strips must be such that when 
the piston leaves the casing 
towards the middle the strips 
shall not drop out. For the 
packing against flat surfaces 
one design uses radial strips 
similarly pressed against the 
flat heads by springs, and the 
other depends upon counter- 
bored holes drilled a short 
distance apart, parallel to the axis within which condensation and 
lubricant will be caught, which will serve by their capillary action 
to prevent any considerable escape of live steam. 

It will be apparent that almost any rotary engine can be reversed in 
principle and become a rotary pump by applying power to the shaft by 




Fig. 456. 



502 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

outside mechanical means and admitting water through the passages 
with which the steam enters in the rotary engine. This convenient 
pecuharity has given rise to a formerly popular form of steam fire- 
engine, in which the steam and water pistons are arranged on parallel 
shafts properly geared together. Such an engine requires no valves 
on its water end, and the water used can be full of impurities and solid 
matter without great inconvenienc3. 

In efforts to compel expansive working of such rotary engines, sliding 
cut-off valves have been introduced but they have not been significant 
or satisfactory. Governing will always be by throttling, either on the 
inlet or on the exhaust. Attempts to use a sliding radial plate as an 
abutment for pressure or as a partition between the admission and 
exhaust-pressures have failed from the demand for excessive effort to 
accelerate the mass of such a plate at the speeds required to get it in 
place soon enough to do any good; and to introduce any reciprocating 
mass whatever is to sacrifice the primary excellence of the rotary 
principle. 

333. Advantages of the Rotary Engine. The arguments to be 
urged in favor of the rotary-engine principle are so many that the skill 
of innumerable inventors has been continuously directed towards 
their design. Among other advantages are: 

1. These engines are adapted for uses where human power will be 
required or used to govern them frequently and quickly, as in hoisting 
and quarry engines; or where variation in resistance is a variation in 
speed, as in marine work; or where sudden cessations of resistance 
at speed are unusual or impossible, as in motor-cars and motor- 
boats. 

2. The effort of the steam is apphed directly without intervening 
mechanisms for conversion of the motion. This avoids their atten- 
dant friction, their costly fitting, and probable lost motion. 

3. There being no reciprocating parts, there is no inertia to be 
overcome at the beginning of the stroke, with the attendant consump- 
tion of energy required to accelerate them. 

4. The engine has no dead-center, but will start from rest in any 
position. 

5. Absence of reciprocating parts makes it easy to run the shaft at 
the highest speed. This has attracted designers of steam-driven 
dynamos to use this type of engine. 

6. The engine becomes very compact from the absence of converting 
mechanism, so that it occupies httle room. 

7. The engine has either no valve-gearing, or that which it has is 
of the simplest character. 



THE ROTARY STEAM-ENGINE 503 

8. These features, and the absence of expensive mechanism, make 
the engine cheap to build and therefore usually cheap to buy. 

9. Absence of reciprocating-rods and dead-centers results in a 
construction in which the presence of condensed steam in the cyHnder 
does no harm. It does not stop the engine from turning, it cannot 
endanger the cylinder-casting, the engine can be started, even if under 
water, by simply opening the valve which admits pressure to it ; it will 
start with solid water. 

10. Its incased construction and the above peculiarity particularly 
adapt it for out-door service and exposed places. Weather does it 
no harm, and its protection from outside injury makes it a serviceable 
quarry motor. 

11. It requires no skill to handle it. If constructed to be rever- 
sible as in Fig. 456, it can be reversed from a distance by simple rope 
and weight. 

333. Disadvantages of the Rotary Engine. The objections to the 
rotary engine are both practical and inherent. The practical objec- 
tions belong to the difficulty of satisfactorily packing surfaces which 
do not move through equal spaces in equal times. Those parts farther 
from the axis move through a longer path in a revolution than those 
nearer to the axis. The wear from abrasion is therefore greater at one 
part than another. When the packing-strips have become somewhat 
worn, leakage ensues, and a noisy rattle from looseness of the fits. A 
second practical difficulty is the expense connected with proper lubri- 
cation of such engines, and the difficulty of taking care of excess of oil 
rejected by the exhaust. If efficiently lubricated, they consume an 
excessive amount of oil. 

The inherent objections to the rotary engine are: 

1. The presence, in the volume to be filled by live steam from the 
boiler, of an excessive waste space which has to be filled by steam at 
each revolution, which steam is exhausted without doing all the work 
there is in it. This corresponds in reciprocating engines to an excessive 
clearance. 

2. The very continuity of the action of the steam upon the rotating 
pistons precludes the possibility with the single rotary engine of work- 
ing the steam expansively, so that when the steam leaves the motor 
it shall have become largely reduced in temperature and pressure by 
doing work with increase of its initial volume. The expansion is 
from the boiler and the water in it, and not from the actual volume 
received by the engine for the work of one stroke. In other words, 
the rotary engine is a non-expansive engine. These two difficulties 
make the rotary engine uneconomical. 



504 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

3. It is difficult to design the rotary engine for large horsepowers: 

First, because the structure becomes inconvenient the moment that 
large areas are desired, so as to make a value of PA in the horsepower 
formula a large factor; second, because it becomes difficult to secure 
the condition of high piston-speed in feet per minute unless the diam- 
eter of the casing be made so large that the difficulties both practical 
and inherent become nearly insurmountable and the advantages of the 
rotary principle are sacrificed. Third, because to secure a large start- 
ing or turning moment from rest the engine has to be made long parallel 
to the axis of the shaft; and when this is attempted structural difficulties 
increase, and the advantage of weight and bulk over the reciprocating 
engine is lost. 

The economy which a single rotary engine cannot secure from its 
inability to work the steam expansively has been sought and secured 
in a degree by arranging rotary engines in series upon a shaft, so that 
the steam rejected from number one engine becomes the driving steam 
for motor number two of larger volume. By this means the steam 
when rejected is at more nearly the pressure and temperature of satu- 
rated steam at atmospheric pressure than can be attained with the 
single rotary engine. This does not even yet secure the advantages 
of expansion in the piston engine, because such increase of volume as 
is secured by simple enlargement of chambers without the doing of 
work upon a mechanical resistance is of the nature of free expansion, 
and results in no economy. The turbine to be discussed in the next 
chapter has so transcended the possibihties of any rotary pressure 
engine in the large sizes, that the importance of the rotary is becoming 
steadily less and less, even for the narrow range of the smaller powers. 

A transition design by the late Captain Ericsson for marine purposes 
will be interesting (Fig. 457A in the Appendix). The piston was a 
vibrating or rocking element, working pendulum-wise through a 
limited arc. The piston keyed to the shaft was in effect directly at- 
tached to the beam center, from which the connecting-rod drove to 
the crank in the ordinary beam method. This engine had two valves, 
admitting and exhausting alternately. 



CHAPTER XX. 

THE STEAM-TURBINE. 

335. Introductory. Historical. The end of the nineteenth cen- 
tury witnessed a return and a renewed recognition of the turbine 
principle for steam-motors. Hero of Alexander made a steam toy- 
before the Christian era embodying the concept of reaction (Fig. 460), 
and Branca in 1629 described the turning of a wheel by the impulse effect 
of a jet of steam from a nozzle (Fig. 461). The modern era began with 
Gustaf De Laval of Sweden in 1883; with C. A. Parsons of England in 
1885; with J. H. Dow of America in 1893; with Rateau of Paris, France, 
in 1894, and with C. G. Curtis of New York in 1896. These basal 
patents have been followed by other and later ones in detail. The 
De Laval nozzle, for instance, dates from 1894, and the Parsons 
governor from 1895. Other names in an historical list would include 
Real and Pichon, 1827; Avery, 1831; Leroy, 1838; Pibbrow, 1842 
Wilson, 1848; Delonchant and Tournaire, 1853; Hartman, 1858 
Monson, 1862, Perrigault and Farcot, 1863; Moorhouse, 1877; Cutler, 
1879; Imray, 1881; Babbitt, 1884; Altham, 1892; Leger, 1894; Fer- 
ranti, 1895; Bollman, 1897, and many others. The names identified 
with manufacture and production are those of Rateau, De Laval, 
Riedler, Stumpf, Zoelly, Brown, Boveri, Holzworth, Parsons and 
Curtis. The Westinghouse turbine is the land design of Parsons: the 
General Electric turbine is the Curtis. 

The principle of the steam turbine is the application to a motor utiliz- 
ing the expansive force of steam, of the methods of making available 
the kinetic energy of water in the Pelton wheel and the water turbine. 
The principle of pressure-action upon a slow-moving piston fitting 
tight in a cylinder bore has been abandoned: instead of pressure the 
kinetic energy of a mass moving at high velocity because of a differ- 
ence of pressure, is made to impart such energy to the revolving receiv- 
ing element or wheel of the motor. Such revolving element is called 
the " rotor " of the turbine, to include a possible succession of tur- 
bines, working in series. The aim has been to utilize to the fullest 
extent the recognized advantages and economy of the theory of 
expansion of steam (paragrafs 295 to 303) and secure the same 
advantages of directness of application of mechanical power which 

505 



506 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

the rotary principle can attain (paragraf 332). The era of high- 
speed machinery for generation of electric energy has been favorable 
to the turbine. The era of the slow-speed pumping-engine, mine- 
hoisting engine, marine and factory engine in the use of power were 
as distinctly unfavorable to its development. Its use for electric 
generation and transmission will steadily increase until the develop- 





FiG. 460. Hero's Reaction Turbine. Fig. 461. Branca's Impulse Turbine. 

ment of the internal combustion engine and its broadening use narrows 
the field for the spread of both the turbine and the reciprocating type 
of steam-engine. 

336. The Mechanics of the Steam-turbme. The steam-turbine as 
a machine to utilize and render available the potential and intrinsic 
energy stored in a mass of hot high-pressure steam, will apply princi- 
ples which fall under two groups. The one is the dynamic group, 
appropriate to the action of the mass and velocity of the steam as a 
fluid, independent of temperature changes; the other the addition 
to these effects due to the transformation of temperature energy into 
mechanical energy in the process of expanding. As a matter of energy 
due to mass and velocity, the turbine utilizes the impulse of the high- 
speed jet, and the reaction effect due to changing the direction of the 
movement of such mass by a force which is used in propelhng the 
rotor. The compounding or stage principle, to use the heat energy in 
stages of reduction of temperature and pressure, and to eliminate 
inconvenient high rotor speeds, and the expanding nozzle principle 
are thermodynamic factors. 

337. Impulse Energy against a Turbine Blade. If the mass of the steam 
coming upon a turbine blade in a second be called M, and the force which accelerates 
it be called F, and the units of velocity added per second, or the acceleration, be 



THE STEAM-TURBINE 507 

called/, then in a time t the velocity generated or V will he Jt: but the space passed 

over (s) while the velocity was changing from zero to V was the product of the 

+ F V 
mean velocity — - — = — and the time t. Hence : 

^ z 

ft . Jt' J • y 

s = ^ X i = ^ and smce — = t, 
s= ^or 7^=2/8. 

The force F will be measured by the acceleration it can produce in a unit mass 
M: or F = Mf. The unit mass is so much matter as the force of gravity will accel- 
erate in one second and produce the standard acceleration of 32.2 feet per second: 

W 
hence for mass can be substituted ^ttt^- » and 

oZ.Z 

W 

In a stream or nozzle passing W pounds per second with a uniform velocity V 

feet per second, it may be considered that a constant force F has acted upon W 

for a second and then ceased. As in the first part of the deduction, the mean veloc- 

V FV 

ity is — and the work of such impulsive force is w^ = —^ • In such a jet acting 
z z 

under the influence of gravity the energy would be Wh, which can be written 



Wh = 



^9 



since h corresponds to s in the general case, and g corresponds to/. 

But if there are no losses, the energy of the jet should be equal to the work im- 
parted to it, or 

FV WV , r. TTF 

— -— = — pr — ' whence F = • 

2 2 g 

In a flowdng stream of area A and weighing D pounds per cubic foot, W pounds 
flowing per second will correspond to DAV. Substituting in the value for F 

DAV^ 



the impulse effect per second varies as the square of its velocity when D and A 
are constant. In steam D varies as the pressure, and is taken from a steam table 
for any assumed case. 

If the force F directs the jet deUvering W against a surface, and there are no 
losses, such surface would require an equal force to hold it still; or the full effect of 
the impulse would be received on that surface. If the jet imparted all its energy 
to the fixed surface, and the mass M had no velocity in the direction in w^hich it 
was moving with, the velocity T', the impartation of energy was complete. But 
there is no work done if the surface receiving impact is moving already with a 
velocity V: the jet did not reach the surface. If the surface receiving the jet was 

WV 

mo\'ing with a velocity Fg the impulse would be L before the surface retarded the 

WV 

iet, and after the surface and jet were moving together at their common veloc- 

9 



508 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

ity. The dynamic effect of the jet on such moving vane of a turbine will be the 
difference between the jet initial and the bucket final velocity; or 

_ W(V, - V,) 
9 



The energy will be the pressure multiplied by the mean velocity, or 
Hence the energy given from jet to bucket will be 

W (7,2 _ y^2) 



E 



2 



which reduces to horsepower by dividing by 550 foot-pounds per second. 

338. Reaction in a Jet and Bucket. If the jet issues from an orifice or 
nozzle in the side of a vessel, the pressure upon an area opposite to the jet must be 
the same as that which prevails in a film or section of the orifice just before the jet 
issues. This reaction pressure is therefore the same as the impulse F, or, 

i2 = i.^EZ = 5AZl. 



If that reaction pressure is made to drive that hitherto stationary surface in the 
direction of the pressure with a velocity having the mean of the sum of the previous 

two or — ^— 2 — — , the energy will be 

2 5^ 
as in the previous case. 

If the difference V^ — Fg be called x, the impulse of a mass M is Mx. If the 
common velocity of wheel and steam when the impulse has been completely absorbed 
be called u, then the work of Mx is Mxu; and if the steam left the wheel at right 
angles to the motion of the blade, this would be the work absorbed. If, however, 
by so curving the blade the mass of steam leaves the wheel not with a velocity u 
laterally, but with a velocity zero, the force to reduce the u to zero appears as a 
reaction against the blade, tending to make it revolve. This force must therefore 
be equal to Mu in intensity, and if exerted through a path u to reduce the velocity 
of the steam relative to the earth to zero, the work of such reaction will be Mu^. 
The total energy is therefore their sum, or 

E.^ = M {xu + u^). 

V 

If the special assumption be made that x = u, and u = ^, 



which is the maximum theoretical value, or gives a theoretical value for the effi- 
ciency of 100 per cent. It is impossible to realize a complete negative velocity of 
u and get the steam out of the buckets. The best which can be done is to get 
it low but finite and positive. 

339. Relation of Jet Velocity to Pressure. In paragraf 337, the kinetic 
energy of a stream of fluid carrying a weight W through a height h was 

2g 



THE STEAM-TURBINE 509 

if V denote the velocity in feet per second of its flow. In a closed vessel of one 
square foot of area of cross-section and of a height h, the pressure in pounds per 
square foot at the zero of height from which h is counted would be Dh when D is the 
weight of a cubic foot at that pressure. Hence when the pressure is counted from 
a zero of pressure, the velocity due to a pressure P in pounds per square foot becomes 



- ^^4- 



If the flow be into another pressure, then the quantity P in the numerator should 
be the difference between these two pressures from the zero of pressure. The quan- 
tity which will flow needs to be corrected for the conditions of practice imposed 
by the shape of nozzle, etc. 

The velocity having been found due to the pressure, the energy in horsepower 
per hour per pound will be 

1 pound X F,2 - F 2 



Energy 



2 ^ X 550 X 3600 



If V be called 3,000 and the velocity on leaving be called zero, 
Energy per pound of steam = 0.07 horsepower per pound of steam or the reciprocal 
of this, 14 pounds of water per horsepower per hour. If the velocity be increased 
by increasing the pressure, the rates improve. 

340. Blade Velocity under the Jets. The assumption of paragraf 338 that 
the best results are secured by making the blade velocity one-half that of the jets 
is supported by computation, and holds when there is no angle between the jet 
and the blade or vein. Fig. 463 shows the De Laval jet angle and the fact that 
such angle exists makes the wheel velocity a little less than one-half. In the single 
stage nozzle-form it is usually 47 per cent. When the drop-down pressure is done 
in one step and the steam has the high velocity thus resulting, the speed of the rotoi 
becomes inconvenient. For example if F = 3000 feet per second, and u for the 
blade is 1500 and the circumference of the wheel one foot, there must be 1500 
turns per second, or 90,000 per minute. Hence the plans of compounding to divide 
the pressure range into steps and lower the tangential velocity. It is hard to find 

material to stand up against the centrifugal stresses 
at these velocities. 

341. Thermodynamic Principles underly- 
ing the Steam Turbine. The steam turbine 
must also withdraw energy from the current of 
steam in the form of heat, as well as of kinetic 
energy. It is in this that its great advantage lies 
over the rotary steam engine, in that by utilizing 
expansion and the heat energy dehvered in the 
process it is a superior heat engine in the more economical exchange of heat into 
work. Turbines utilize expansion in two ways; by the expanding nozzle, and by 
the expanding volume secured by compounding. 

Repeating the deduction of paragraf 309 for the work in expanding when no 
heat is added to the steam in the form of heat, and relating it to Fig. 462, it will 
be remembered that the work in expanding from p^v.^ to the condition of Pi^^z in 
this case was 




510 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

If the volume Vg be extended to infinity toward the right the value for its work 
capacity reaches its limit, or is the total intrinsic energy of such a weight of steam. 
When V2 is infinity the work becomes 



-1 ' 
which is an expression therefore for the intrinsic energy. At the condition B it is 

as above; at the condition C down the line of expansion it is H^ = ^ - " • 

n — 1 

If the steam or other gas be confined in a vessel fitted with an outlet nozzle, and 
the intrinsic energy in the vessel per pound be called Zj, and that in the nozzle be 
called I2, external work is done upon the gas inside to get it to the orifice and give it 

a kinetic energy r-^ ; and each such pound does the external work of expanding to 
^ 9 

V 2 
P2 and V2 in the nozzle, and its state of kinetic energy is then j^ • LTnder the law of 

zg 

adiabatic flow assumed for the steam, with the heat or total energy the same at the 

beginning and end by the principle of the conservation of energy 

72 y 2 

h + Vi'^i+ ^ =^2 + Vi^2 + 27 • 

It is proper to neglect the velocity within the vessel as so small as to be of no 
consequence when the vessel is of any size, so that the kinetic energy at the nozzle 
can be written 

— - = Zi - Z2 + p,v^ - p^v^. 

z g 

But if it be assumed that there are no nozzle losses nor friction transfers, the 
second member represents the algebraic sum of the interchanges of internal energy 
and external work when the pound in question was expanding from a state PiV^ to 
the state ^2^2- These changes are by the hypothesis due only to the work done by 
the heat energy in imparting kinetic energy; hence the numerical value of the 
expression for the kinetic energy is the same as that of the heat given up per pound 
in such expansion. If for the quantities denoting the internal energy the total heat 
from steam tables be substituted, and the difference in heat units per pound be 
multiplied by 778, the product will be the energy in foot pounds per pound ; or 

y2 
Energy in foot pounds per second = — = (ZZ^ — H^) X 778. 

If for the quantities Z^ and I^ the value for the internal energy be substituted as 
deduced from Fig. 462, 

Applying the law for the perfect gases, p{v^^ = ^2^2"^ and reducing 



which may be compared with the expression for work in terms of pressures in the 
piston motor of paragraf 309, If the area of the orifice be A as before, the volume 



THE STEAM-TURBINE 511 

discharged per second is AV. If fg be called the volume of a pound of steam at the 

AV 
pressure p^ taken from the tables, the weight per second will be ; hence mul- 
tiplying the value of V by A and reducing, 

Weight per second W = 



-^V(^)(^)fe)"^gf] 



This is a maximum when the quantities under the square parenthesis are a max- 

;mum. If — be called r, and its maximum found, it becomes 
Pi 



(ri^)" 



The exponent 7i is the ratio of the specific heats of steam at constant volume 
and pressure, and if its usual value of 1.135 be taken the maximum flow will be 

when — = 0.577. This is for straight-sided nozzles. Experiments have shown 

Pi 
that as the back pressure is reduced in outflow researches, the flow by weight reaches 
a maximum for steam and that thereafter further reduction does not increase the 
flow. If Pi be increased with p^ fixed, the weight of flow increases. This confirms 
the general truth of advantage from high initial pressures. With diverging nozzles 
the ratio increases up to complete exhaustion. The gain from superheating with 
steam turbines is both thermal and mechanical. The mechanical gain comes in 
from eliminating fluid friction on the blades and their mechanical erosion at high 
speeds of flow from drops of water due to condensation. Turbines work more 
effectively condensing than non-condensing, by reason of the lowered value for p^. 
It would expand the present available space unduly to carry this treatment further 
to include the facile and useful deductions from the use of the temperature-entropy 
diagram. For example, if the entropy-factor have a value of E^ and E2 corre- 
sponding to the conditions of pressure p-^ and pa and temperature absolute T^ and 
7^2 the maximum velocity in a nozzle shaped to give an adiabatic expansion would 

be * 

V = 158 V(E, + £■.,) (T, - T,). 

Much experimental work on the flow of steam through nozzles and the best path 
for the expanding jets has been done by manufacturers and others. Similar tests 
are the only means of finding the coefficients with which the theoretical computations 
must be multiplied to conform to actual net output of work. 

345. Single-stage Expansion-nozzle Turbine. The De Laval tur- 
bine of 1885 and 1894 is the simplest and most direct example of the 
type having an adiabatic expansion of steam in one or more nozzles 
from a p^ of initial pressure to a ^3 ^^ the issue upon the wheel and 
using only one set of blades and one wheel. The nozzle is so propor- 
tioned that the velocity increases as the pressure falls, so that the 

* From " Steam Turbines " by Prof. Carl C. Thomas. John Wiley & Sons, p. 70. 
Consult also Stodola, Treatise on the Steam Turbine. 



512 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

steam has just enough pressure to overcome friction on the blades and 
carry itself through the wheel (Fig. 464), and escapes to the low-press- 
ure or condenser side with the least energy in the pressure form. Such 
energy has been transformed into kinetic energy and the mass of steam 




— anaiua 

F 



Fig. 463. 



at high velocity impinges on the curved blade, and produces its 
impulse effect. By curving the blades, as in the Pelton impulse wheel, 
a certain reaction is elicited, and the steam leaves the wheel with little 
energy either in pressure, heat or velocity. The limit of the number 

of nozzles (Fig. 465) is only set by 
the convenience of getting them in, 
and keeping their jets from interfer- 
ing with each other. Fig. 463 shows 
the control of the jet or nozzle by 
a hand-wheel to vary M, without 
varying the velocity in the nozzles 
which are in action. The nozzle, 
being designed for a particular re- 
lation of Pi to p2> will ^ot work 
as efficiently with another ratio. 
Hence control should not be by 
throttling the steam pressure, but 
by varying the weight entering the 
chamber D at the computed pres- 
sure, and passing the nozzles. 
When the engine is changed from 
condensing to noncondensing at any 
time the nozzles should be changed also, but the construction makes 
this easy to do. 

The high velocity of the issue of steam, even if that of the blades is 
one-half of it or less, makes an inconvenient velocity for the periphery 
of the wheel as respects withstanding centrifugal accelerations: and 




Fig. 464. 



PLAN 

De Laval Turbine. 



THE STEAM TURBINE 513 

the number of revolutions of the shaft is too high to use without reduc- 
ing by gearing. A gearing ratio of 10 to 1 is made a feature of these 
designs, integral with the machine, so that the shaft from which the 
power is taken off shall turn at 2000 revolutions or thereabout for a 
turbine element itself at 20,000. To provide for the running balance 
of such a high-speed element, and keep it cool and silent, the rotor- 
shaft is made of very tough steel, but of so small a diameter that it 
will flex under any lack of homogeneity of the rotor, and let the latter 
revolve around an axis through its actual center of gravity without 
undue stress upon the bearings. The rotor itself does not touch the 




Fig. 465. 

casing anywhere, and needs no oil, nor has it any friction. The bear- 
ings, however carefully designed, must be very carefully watched to 
see that they are copiously oiled, since if one gets dry for even a few 
seconds, its integrity is gone, and perhaps extensive repairs are en- 
tailed. The bearings wear rapidly also in careless hands, and noise 
and inefficiency begin at once. The rotor cannot be of large diameter 
to reduce the number of revolutions, because centrifugal accelerations 
and stresses increase with the diameter (paragraf 260) and no material 
has been found with tensile resistance sufficient to hold against the 
tearing effect. 

346. Single-stage Impulse and Reaction Turbine without Expansion 
Nozzle. Riedler-Stumpf Early Types. The impulse and reaction 
water-wheel known as the Pelton wheel served as an early starting 
point for many designs, having simplicity and cheapness of construc- 
tion for their advantages. They have been superseded in every success- 
ful case by the compound types, to reduce the inconvenient speed. 
They have been successfully applied in smaller sizes to driving centri- 



514 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

fugal pumps — often in two pumping stages — centrifugal fans and 
blowers, centrifugal drying and cream-separating machinery and elec- 
tric generators. The high speed gives small size and bulk both to 
motor and driven machinery. Rateau, Richards, Levin, Zoelly and 
Kerr have all applied the Pelton double cup-shaped bucket to steam- 
turbine design. 

347. The Pure Reaction Turbine without Impulse. The turbine of 
J. H. Dow (Fig. 466) is an example of the pure reaction principle with- 
out impulse. The superior mechanical efficiency of the types embody- 




FiG. 466. 



ing both impulse and reaction have put these latter to the front in the 
larger sizes. For simple high-speed work against low resistances to 
rotation these machines are compact and cheap. The steam enters 
in the smaller annulus close to the shaft and expands in volume and 
in velocity as it works from ring to ring. The modern forms put the 
successive elements at the side of each other, instead of radially. 

348. Compound Turbines. Multicellular Type. The advantages of 
dividing the expansion process, down pressure and temperature into 
successive stages commended themselves at an early day. The prin- 



THE STEAM-TURBINE 



515 



ciple one is the reduced wheel velocity, and the reduced surface velocity 
of the steam upon the metal of the blades. This latter occasions not 
only excessive fluid friction, but worse than this, a rapid mechanical 




Fig. 467. 

erosion. Water-drops in the steam act as the sand particles in a 
sand-blast at these high speeds. The compound principle has been 
embodied in two general types. In one, there is a succession of wheels 




Fig. 468. 



of the same diameter in separate compartments, the steam moving in 
succession with increasing volume and reduced pressure. In the other 
the wheels are of increasing diameter, and either in the same enclosing 
casing, or in one divided into a small number of compartments, much 
less than the number of wheels. 

An interesting and successful American type of this class is the Kerr 
turbine of Figs. 467, 468, 469. The steam enters past the throttling 



516 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

governor into a ring-shaped channel in one head, from which nozzles 
direct the jets of steam upon the double-cup or Pelton type of buckets 
on the revolving disk. Between wheel No. 1 and wheel No. 2 is a cast- 
iron stationary dished diafram (Fig. 467), and the steam is again 
directed by a second set of nozzles upon the buckets of the second 
wheel. The nozzles increase in cross-sectional area down-pressure 
with the increasing volume and velocity, until at the discharge from 
the last compartment the energy to be rejected has become only just 
enough to carry the steam away after it leaves the last wheel. The 
step reduction of pressure lowers the velocity range in each compart- 
ment: the number of compartments is adjusted to the initial pressure 
proposed. The buckets increase in size — not in number — as the 




Fig. 469. 



volume increases (Fig. 468) and the mechanical or manufacturing 
detail is simple and direct. There should be no side thrust on the 
wheels (Fig. 469) because the jet effect is balanced in both directions, 
and the bearings are so constructed as to keep the wheels in line with 
the jets and secure effective oihng by the ring-system. In this same 
class or type are the newer Rateau turbines of Paris and America; 
the Zoelly of Zurich, Switzerland. With a view to securing divided 
steps of expansion and cheapness of construction by avoiding the 
multicellular chambers along the shaft, the same result is sought in 
the turbine of Fig. 470.* Here the wheel is so enclosed in the con- 
struction of the casing that the successive cells or chambers are seg- 

* Terry Steam Turbine; Hartford, Conn., U. S. A. 



THE STEAM-TURBINE 



517 



mentally disposed, instead of being side by side. The initial steam, 
after acting upon the part of the wheel exposed to it, passes into a 
stationary reversing chamber confronting it, and from this is succes- 
sively returned four times or more to the wheel in succeeding segments 
in its periphery, until it escapes into the exhaust chamber from the 
last. The successive divisions of the expansion into stages enables 
the speed at the buckets to be kept down to 250 feet per second; the 




Fig. 470. 



machine has its bearings close together and occupies the least area of 
ground-plan. These types are much used in small electrical, pumping, 
and fan-blower installations. 

In the Zoelly Swiss designs, the successive wheel disks have been 
grouped into two casings, separated enough to get a bearing between 
in large sizes. The steam from the higher pressure set crosses over to 
the head of the low^er pressure casing through a pipe. By keeping the 
drop of pressure in each step less than the limit of 0.577 of the pressure 
in the compartment previous (as discussed in paragraf 341), straight 
nozzles and cheap to manufacture can be used without interfering with 
the expansion process. 

349. Reaction in Steam Flow from a Stationary Guide Ring. Stator 
Rings. The cup-shaped buckets of all the turbines make use of the 



518 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

dynamic principle of reaction whenever the steam leaves the bucket 
at an angle less than 90° with that at which it entered, so that 
the deflecting force to change the direction of flow has a component 
parallel to the plane of the motion of the wheel and in a direction 
opposite to the rotation (paragrafs 337, 338). In Figs. 463-465 no 
attempt appears to direct the energy of the issuing jet as it leaves the 
bucket because it was assumed to have given all its kinetic energy to 
the w^heel in its passage. 

In the compound types, however, it will be obvious that a consider- 
able potential energy resides in the steam after leaving the first wheel 
in a series, and if such energy is allowed to expend itself in causing 
unutilized motion of the steam in clearance volumes between such 
rotating power elements, to this extent is this motion wasteful. It is 
the purpose in the design of what are called the /' compound reaction " 
turbines to direct the flow of steam from the reaction discharge of each 
wheel into definite channels, and preclude losses by eddies or free expan- 
sion. The steam is received from the rotating vane, moving in the 
wrong direction, and is deflected by the shape of guide channels in such 
a stationary ring so as to be guided correctly upon the buckets of a 
second revolving ring less only the loss by skin friction. Using the 
fixed guide-blade walls as abutments, the pressure and velocity are 
exerted upon the second wheel, and the steam received into a second 
fixed ring of guides and so on. The fixed rings or diaframs carrying 
the guides will form part of the enveloping casing; the revolving rings 
making up the rotor are fast to the revolving shaft. This idea of 
securing a reaction for the kinetic energy and utihzing it again with 
least loss is the basal conception of the Parsons turbine (Westing- 
house) and is also embodied in most of the other compounds. It 
appears in two general forms. In one type there is no impulse and 
nozzles are not used. In the other the impulse principle is availed of 
by incorporating the nozzle feature. Where there are no nozzles, the 
turbine need not be subdivided by partitions into stages. In the 
nozzle type this will usually be done. 

The examples of the compound reaction without nozzles are the 
Parsons- Westingho use and the Allis-Chalmers types; and the Holz- 
worth of America, and the Willans and Robinson of England. The 
impulse or nozzle reaction compound is represented by the Curtis 
(General Electric), the Crocker- Warren, of America; and the Brown- 
Boveri, the Sulzer Bros, and the Lindmark of Europe. 

The diafram or ring which carries the deflecting guides between the 
wheels which carry the buckets can be slipped on over the ends of 
the shaft in small sizes alternately with the wheels and be locked to the 



THE STEAM-TURBINE 519 

casing when the latter is all in one piece or continuous. In larger sizes 
it is convenient to split the casing along the meridian or greatest dia- 
metral section into two halves. Here the guide ring will split with the 
casing to which it is secured. The guide-blade ring as the element 
fixed in position has been called with the casing, the " stator " to dis- 
tinguish it from the revolving element or " rotor." 

350. The Westinghouse Compound Turbine. The Westinghouse 
Company bought manufacturing rights from C. A. Parsons in 1895, and 
introduced the American product with their modifications in 1899. 
Fig. 471 is a vertical section. In the form shown the rotor element is 
made in three diameters, in order that the variation in size of blades 
may be reduced to convenient steps, and keep the variation of steam 
velocity and wheel velocity under it within proper ratios. The steam 
enters at ;S through a balanced regulating or throttle-valve controlled 
and operated also by the governor. It enters the turbine passages 
proper in a complete annular channel between the casing and the 
solid part of the rotor, and moves to the left past the alternate fixed 
and revolving blades until the space B is reached, from which it passes 
to the condenser or to the open air. The depth of the blades is made 
to increase continuously in each stage or diameter to provide for the 
expansion. 

Since the pressure at A is so much greater than at B and the flow 
of steam produces reaction components, there is a tendency to end 
thrust upon the rotor as a whole. This is met by balance disks or 
pistons PPP connected directly to the chambers of increasing diam- 
eter by open passages EEE to reduce this to a minimum. The pistons 
do not touch the casings, and are kept steam-tight by a succession of 
rings and ribs whicl^ do not touch, but form a labyrinthine or circuitous 
channel through which only an inconsiderable leakage takes place if 
any at all. To keep the rotor blades from colliding with the stator 
guides a small thrust or adjustment bearing T at the right is fitted with 
collars to keep the standard clearance. This is an eighth of an inch 
in small sizes, and increases up to one inch in the larger. It will be 
obvious that great injury can be done to the rotor from a broken 
blade getting astray in the clearances. 

351. Governing and Overload Capacity in the Westinghouse Turbine. 
It is very desirable that the control of the weight of steam entering the 
turbine should be direct, and not by means of throtthng the pressure 
and leaacing kinetic energy and velocity more than the pressure. Hence 
tue supply to the rotor is made intermittent or pulsating by causing 
the balanced valve V to rise and fall at intervals, letting full pressure 
and velocity reach the wheel and then shutting off all supply. The 



520 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




THE STEAM-TURBINE 



521 



valve V is raised by steam pressure admitted below a piston (Fig. 471 
at the left) and is quickly closed by the spring. The spindle at the 
right of Fig. 472 is driven by an eccentric from the worm wheel at the 
extreme right of Fig. 471. The governor by shifting the position of 
the fulcrum of the longer lever which drives the pilot valve of the 
main valve piston makes the lifting steam open pressure sooner and 
cut it off later per stroke of the eccentric in one set of conditions: and 
in the other set, the pilot valve is opened continuously and the piston 




Fig. 472. 



never fails to close the steam admission completely. In this case, the 
pulsation action disappears and the steam enters continuously. 

When now the demand for steam exceeds the capacity of the valve 
V and the annular space through which steam enters the high-pressure 
end, the capacity of the motor is reached, and there is no means for 
providing to meet a temporary or continuous overload call. This is 
met by the use of the supplementary valve F, operated also by the 
governor, and having also a hand control. When the demand comes 
for more energy, V2 is opened and allows a bleeding of high-pressure 
steam into the No. 2 stage of the rotor, where it acts with a larger 
turning leverage than in the chamber A. This can also be used in 
starting if the resistance torque is large. The pilot valve mechanism 
of this by-pass valve is just the reverse of that of the main valve: when 
the pilot is opened, allowing pressure in the connecting pipe to escape, 
the pressure of steam upon the valve piston causes it to open against 
the spring pressure. 

Fig. 473 shows the general perspective of a Westinghouse 3000 kilo- 
watt turbine generator. Lubrication is effected by a pressure feed 



522 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




THE STEAM-TURBINE 



523 




524 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

through channels in the bearings from a pump driven by worm gear, 
and fitted with a cooUng coil to keep the oil temperature down so that 
it can be repeatedly used. Packing of the joints where the shaft leaves 




Fig. 475. 



the heads of the casing is secured by a water-seal device, where a set 
of vanes or blades revolve with the shaft in an annular chamber forcing 
the water radially outward by centrifugal force. The left hand end 
has to resist indirectly the tendency 
of air to rush in and break the 
vacuum: and the right hand end is 
connected to the same lowered pres- 
sure by the balance connection E. 
The water can be renewed as re- 
quired, and no parts are in metalhc 
contact to rub on each other. 

352. The Allis-Chalmer's Com- 
pound Turbine. This type is made 
also under the Parsons basal designs 
for a compound reaction machine 
(Fig. 474). It differs from the pre- 
ceding in constructive and manufac- 
turing detail. In Fig. 475, for ex- 
ample, which is a diagram only, the 
balance of end-thrust is produced 
by two areas at the right hand and 

by one (Z) at the left, the latter working in a supplementary cyHnder 
W. In this latter at the surface Y the same pressure prevails as at 
X, and the small annular area forcing K to the left is balanced by the 
larger area forcing it to the right. The blading is also different (Fig. 
476), both for manufacturing reasons and to remove a tendency to 




Fig. 476. 



THE STEAM-TURBINE 



525 



inconvenient tremor and vibration when the tips of the blades were 
not confined and strengthened by an enveloping ring. The features 
of governing, overload capacity, packing, and lubrication are met satis- 
factorily along accepted lines. 

353. The Curtis Nozzle Compound Turbine. The Curtis turbine 
embodies the two ideas of expanding in a diverging nozzle, securing 
impulse effect, and the compounding principle of expanding in several 

steam Ckest 




U«i<«i<(«<<<iiii^ 



Moving Blades 
Stationary Blades 
Moving Blades 
Stationary Blades 
Moving Blades 




Nozzle Dlaphiagm 



Stationary Blades 



cccccccccccccccccccccc 



Moving Blades } ))l 



— ~ I<«t«««<««««c«l 

Moving Blades | ])))) h \)}\) ]) HY) h ]) D^D )) D h}) D h l)i 



11 11 



Fig. 477. 



stages. For the latter it utilizes the reaction principle of the Parsons 
type, having alternate fixed and moving elements of guide-blade and 
bucket.* The turbine is made in two differing forms for land and for 
marine service. The former rights are held by the General Electric Co. 
Fig. 477 shows the type arrangement of the principle. The steam 
passes through individual nozzles each controlled by its own valve. 

* Mr. Charles Gordon Curtis studied engineering at Columbia University, graduat- 
ing in 1882. In 1907 his creative and practical achievements were recognized by 
the honorary degree of Master of Science. 



526 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




Fig. 478. 



THE STEAM-TURBINE 527 

These nozzles are as numerous around the circumference as the weight 
of steam required calls for. The weight is controlled by closing off 
individual nozzles without throtthng effect. It passes through the 
nozzles undergoing expansion and increase of velocity with a lowering 
of pressure as in the pure nozzle type, and acts by the reaction system 
upon the succession of wheels which carry the buckets. The principle 
of stage expansion is carried out in the larger sizes, each stage having 
its set of expanding nozzles. For example, if there be four stages in 
the expansion process, with two revolving wheels in each stage, which 
is a very usual and successful proportioning with 150 pounds pressure, 
the drop will be from 150 to 58i pounds in the first nozzles, calling for 
a linear velocity of 2000 feet per second. After passing through the 
first wheels the steam enters the second set of nozzles, in which if ex- 
panded to 18^ pounds the terminal velocity will be again 2000 feet 
per second, due to the increase in volume. A third set of nozzles 
with their wheels will result in a velocity of 1600 feet per second with 
a reduction to 3^ pounds pressure; and the final nozzles and the fourth 
pair of wheels will give a pressure of 1 pound above vacuum, and a 
velocity of 1400 feet per second, at which the residual energy will be 
just enough to carry the steam away. 

The constructive advantages for electric generators on land which 
are offered by putting a short turbine such as the Curtis with its shaft 
vertical, early attracted designers to this plan. The stationary part 
is symmetrical in shape, easily moulded and cast, and free from irregular 
disturbance by heat. The structure of the casing forms convenient 
and adequate support for the generator. Much floor area is saved, and 
the building will have height in any case. Cost of foundations is 
reduced in reduction of ground plan, yet with adequacy of support, 
since alinement is not specially vital. Accessibility all around the 
machine is secured. The shaft bearings are relieved from the stresses 
of the weights to deflect them, and their lateral friction is negligible. 
Hence the shaft does not have to be so massive to prevent distortion: 
bearings can be placed where convenient. With an adequate step- 
bearing the relative positions of fixed and revolving parts are definitely 
fixed, and the short length prevents the inconvenient change of posi- 
tion of parts due to expansion. Fig. 478 shows such a vertical turbine 
in elevation and section and Fig. 479 enlarged detail of the stages. 
In the vertical machine, the weight stresses are transferred from 
horizontal bearings of the other types to the foot-step bearing: but the 
friction herein can be made definitely and positively a fluid friction 
and the shaft be compelled to float upon an oil film. Fig. 480 is a type 
of turbine footstep. The block A on the end of the shaft is of cast 



528 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

iron and turns with the shaft. The similar cast-iron block B is kept 
from revolving and is adjustable vertically by the heavy screw S. 
Both blocks are recessed on their faces at C for about one-half their 
diameter to form an oil cavity supplied by pressure from below through 
the pipe D. The blocks separate when the pressure is great enough 
to balance the weight, and oil flows outward and then upward between 




Fig. 479. 



the shaft and the steadying bearing to an overflow from which it 
escapes. The oil pressure is kept constant by an accumulator, so that 
flow should not cease if the pump stopped. The pressure varies with 
size of the generator: with a 5000-kilowatt machine it is made about 



THE STEAM-TURBINE 



529 



1000 pounds per square inch. Water may be used instead of oil. The 
pump is usually electrically driven. 

The Curtis turbine is also made for horizontal shafts, as is required 

for marine practice. This 
p-:^^^r5--^ will be referred to in a later 

— paragraf. 

354. Governing and Over- 
load in the Curtis Turbine. 
The smaller types of Curtis 
turbine are governed by 
throttling. In the larger 
sizes each nozzle or group of 
nozzles is controlled by its 
own poppet-valve, opened 
and closed by the governor. 
The actuation of the groups 
of poppet-valves may be 
effected by a hydraulic 
piston, whose valve is con- 
trolled by the governor, or 
the transmission may be 
mechanical by pawls or 
dogs ; or an electrical system 
can be used, the valve 
spindles being surrounded 
by a solenoid coil whose ac- 
tion balances a spring. As 
more or less current passes in the solenoid, the spring is strained 
more or less, and the valve shut or opened correspondingly. 

Overload capacity is secured either by making the number of nozzles 
for the first stage larger than is necessary for the normal load, and 
having the extra steam capacity available to meet the call for greater 
weight of steam, or by-pass valves may be used as in the Parsons, to 
bring an extra pressure and velocity further down the series. The 
valve at the left in Fig. 478 is a by-pass valve to give the operator 
control of the pressure after the first stage. 

355. Low-pressure or Exhaust Steam-turbines. The high velocity 
with which steam, even at low-pressure, rushes into a vacuum has been 
utilized in making a sort of compound engine or continuous expansion 
system in which the exhaust from a large reciprocating engine non- 
condensing, running intermittently, is passed to a condensing turbine 
running continuously. Such engines are the hoisting or winding 




Fig. 480. 



530 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

engines in mines, and the reversing or continuous rolling mill engine 
in steel works. Heat which would otherwise be wasted in the 
exhaust from such engines is saved and used. The range of temper- 
ature corresponding to a pressure range from atmospheric pressure 
down to that corresponding to 27 inches of mercury vacuum pressure 
(1.6 pounds per square inch absolute) should give an electrical horse- 
power for each 31 pounds of steam so used in driving a generator. For 
each 1000 pounds of exhaust steam rejected, therefore, there could be 
gotten over 30 horsepower if thus utilized. 

This system requires an accumulator between the two engines to 
receive any excess from the one engine, and to keep the turbine going 
during intermissions of exhaust supply. Such accumulator is a heat 
storage reservoir, and either water alone, or cast iron with water is 
the cheapest available material. In the former case the exhaust steam 
passes directly into water, which it heats and makes into steam without 
loss except that due to radiation: in the other, the water is in shallow 
cast-iron trays, and the steam surrounds all as in an open feed-water 
heater (paragraf 227). The capacity for such accumulator will be 
computed by assuming the weight W of steam per hour to be supphed 
to the turbines, and a time t during which no heat reaches the chamber 
from the exhaust. Then since each pound of water at atmospheric 
pressure can absorb 966 units of heat, the heat capacity in B. T. U. 
for each permitted degree of temperature rise or fall will be: 

TF X ^ X 966 
Heat capacity = B.T.U. per minute = H. 

If the permissible temperature range be a number of degrees r = 10 
or more, the weight of water will be 

TT 

Weight of water = — • 



The output from such compounding of reciprocating engine already 
installed and a low-stage turbine is much greater than the increase 
due to attaching a condenser to the former engine. The results of 
tests seem to show such increased output to be over twice what the 
appHcation of condenser alone would give (paragrafs 306 and 501). 

356. The Steam-turbine for Marine Use. The convenience of oper- 
ating condensing apparatus at sea, and the great advantage to the 
turbine when it operates condensing have added to other advantages 
of the turbine for vessels. The absence of vibration at speed, the 
lowered center of gravity, the diminished attendance, the lessened oil 



THE STEAM-TURBINE 



531 




532 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

consumption, bulk and weight, the less danger from racing when the 
screw rises toward the surface should all be listed as advantages, and 
the fact in particular that probably the great increase in propelhng 
power demanded to meet increased speeds in transatlantic passenger 
service could not have been met by reciprocating steam-engines within 
the available limits of space. 

As against these must be placed the high speed of the screws and the 
fact that the steam-turbine does not reverse. The high speed of the 
screws compels a small diameter and small surface for the screw blades, 
and introduces a source of inefficiency (called cavitation) because at 
excessive speeds the water is forced backward faster than it will flow 
around the circle described by the tips of the blades, leaving an area 
of lowered density behind the wheel, instead of solid water for the 
reaction to be exerted on. This may be met by enlarging the turbine 
diameter, when the economy of room and weight vanishes. The gain 
in weight seems to be about 5 per cent. The diminished area of the 
blades of the high-speed wheel diminishes the promptness of the response 
of the ship to manoeuvering needs in harbors, and lowers the holding 
power as compared to big screws of large surface. The non-reversibil- 
ity requires additional turbines for backward motion and manoeuvering, 
and these are a drag in forward motion if separate and not driven 
forward in normal use. If many turbines are used as is the usual 
solution, those close to the hull at the sides are usually the reversing 
ones, and in reversing these are not efficient, detracting from manoeuvring 
power. The turbine is not efficient at speeds below the normal or max- 
imum: hence for cruising in naval work the practice in certain forms 
has been to have special cruising turbines, with their added weight and 
room. The turbine battle-ship gives a very steady deck from which 
to range and fire the big guns. 

Fig. 481 shows plan of the six turbines required to operate the four 
screws of the Mauretania on the transatlantic service. The two outer 
shafts are the high-pressure ahead turbines, and the two inner ones are 
the low-pressure. On these latter are two independent turbines taking 
steam directly for going astern. In backing the high-pressure turbines 
and wheels are not in use, or the arrangement of Fig. 482 may be 
used, with eight turbines on the four shafts, and two additional tur- 
bines to give intermediate pressure ranges for economy at slow speeds 
while cruising as in war-ship conditions. Fig. 483 shows a Curtis hori- 
zontal two-shaft four-turbine design of same capacity and guaranteed 
superior economy. The marine turbine cannot operate any of its 
auxiliaries itself, but these must all be independent (paragrafs 145 to 
151 and 500 to 530). Fig. 481 shows the number and multipHcity of 



THE STEAM-TURBINE 



533 




60 ft.- 



FiG. 482. 




Fig. 483. 



534 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

such auxiliaries in a marine power plant. The condensers for turbines 
will be discussed in a later chapter. 

357. Advantages of the Steam Turbine. The steam turbine has 
advantages over the rotary steam-engine, and also those w^hich both 
offer as compared with the reciprocating engine. In the first class are: 

1. It secures the advantages of expansive working. These appear 
in economy of fuel and low water rate, or in general higher thermal 
efficiency. 

2. There is no piston friction, no need for cylinder lubrication, no 
piston packing, no leakage past pistons, no wear. 

3. It has no limits of size or effective capacity, but the larger the unit 
the more effective. 

As compared with a reciprocating type of motor: 

4. There are no reciprocating masses to be stopped, started, and accel- 
erated and retarded. 

5. The power is applied directly to produce rotation, without the 
friction of joints in a mechanism. 

6. Continuous rotary motion eliminates danger from entrapped water 
in the cylinder. 

7. Foundation weight and mass are reduced, as there are no shaking 
forces resulting from changes of direction of motion of masses, or 
steam effort within the casing. The foundation work is simpler and 
less costly, as there are no fly-wheel pits, etc. 

8. Valve gearing disappears, or what remains is of the simplest type. 

9. Superheating and its thermal economy is easier to apply, since no 
trouble is caused as respects lubrication within the cylinder and defor- 
mations of castings due to a high temperature. 

10. Maintenance and up-keep are diminished where there is no 
metallic contact of pistons and bore, valves and seats. There are no 
pin joints needing adjustment for wear, with knocking and pounding 
after wear begins. 

11. There is no kinematic dead-center, nor need for a mechanism to 
" bar " the engine past its points when the valves are closed. 

12. The angular motion of the shaft is uniform and regular per 
revolution, without the disturbing effect of variable effort on the pin 
with high expansion. 

13. This favors close regulation to speed. 

14. The avoiding of cylinder lubrication makes the condensed 
water in condensing types free from oil without expensive appliances 
to make it so. 

15. Wear or indifference as to adjustment does not seriously affect 
the steam economy; settling of foundations does not affect ahnement. 



THE STEAM-TURBINE 535 

16. The erection is therefore cheap and rapid. 

17. The time to get the machine going from rest and in a cold state is 
less than with the reciprocating engine of same capacity; the operation 
of starting is simple. 

18. The rotor is its own fly-wheel, and the weight and space for the 
latter are saved, while angular regulation is secured and retained. 

19. The cubic space occupied in ground plan and elevation is less 
for the turbine than for the reciprocating engine, and the weight less. 
The values to be given to this advantage will be determined by the 
two sets of conditions chosen, and whether the shaft may be revolved 
at high speed or not. As respects marine conditions of older type as 
compared with modern turbines it would appear that with steamer 
engines of the ordinary marine type the weight will be from 300 to 
500 pounds per horsepower, and in high-speed naval practice about 
150 to 165, with a present limit of 42 pounds. A turbine of the 
Parsons type weighs in the neighborhood of 30 pounds per horse- 
power. The reduced weight of the moving parts helps to keep the 
friction low. 

As compared with gas engines running down to much less than this per 
horsepower — say 10 to 20 pounds and less when speed is high — 
this would prove only a provisional argument. When the turbine 
must reverse, as in marine practice, the gain in weight diminishes for the 
plant as a whole, or where the number of shafts multiplies. The more 
elaborate installation of auxiliaries also tells against the turbine, while 
still leaving the margin in its favor. Transatlantic steamers have a 
margin of 10 per cent gain in weight. 

But the gain in space occupied is more apparent. Fig. 484 is based 
upon a 1000-kilowatt horizontal turbine as compared with an engine of 
cross-compound Corliss type, with the generator between the cylinders, 
the latter being 28 and 56 inches by 48-inch stroke, turning at 95 revo- 
lutions. As the unit increases in size, the comparison becomes more 
favorable to the turbine, and particularly if the compact vertical type 
be chosen. Fig. 485 is the equation of a slow-speed massive engine 
of horizontal vertical type giving 5000 kilowatts with the equivalent 
Curtis. The best case for the reciprocating engine is a high-speed 
vertical cross-compound, compared with a horizontal turbine. The 
worst case for the turbine is a slow speed of shaft with the necessity for 
reversing imposed. The boilers and much auxiliary machinery will be 
the same. 

20. The attempt to reverse at speed does not endanger the structure 
of the engine. 

21. In marine and warship conditions, the low head-room required 



536 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

lowers the center of gravity, increases stability, makes the engine less 
vulnerable behind incomplete armoring, and increases a cargo capacity. 



Horizontal Corliss 



-^^yeilical Cdiliss; 



Vertical Corliss 



■m^$$<m^)^^<w^^mm.^ 



Floor Span 



Fig. 484. 



Head Boom 




The smaller diameter of the wheel at high speed lessens the draft of the 
vessel and enables high speed to be secured if the motor is powerful 
enough. The weights and diameters of wheels and shafts are diminished. 




Fig. 485. 



It would seem that shaft limits had been reached with reciprocating 
engines, and that to get required speed and power through two shafts 
and wheels would have been scarcely possible, and there would not have 



THE STEAM-TURBINE 537 

been room for four reciprocating engines below decks in the big ocean 
liners. The absence of vibration is a great feature for a passenger vessel. 

22. The avoiding of contact surfaces, and the keeping of unbalanced 
pressures off from the moving surfaces, make the manufacturing process 
a simpler one and the equipment for it less varied. 

23. The economy of coal and the purchase and operating costs will 
be discussed in a later paragraph. 

24. The turbine runs economically over a wide range of loading, 
from less than its normal load to a considerable overload. The recip- 
rocating engine has a most economical load, and does not do its best 
on either side of this (see Fig. 486 and paragraf 303). 

358. Disadvantages of the Steam Turbine. The disadvantages of the 
turbine have differing significance according to the uses to which it is 
to be put and the standard used for comparison : 

1. It does not normally reverse. When reversing is a necessary 
feature it must be gotten by a separate rotor with guides and buckets 
set for such reverse motion, either on the same shaft or capable of being 
geared to it. Separate piping and valves must be provided. 

2. It has not a large starting torque or turning moment at low speeds 
to overcome heavy resistances in getting under way. These are the 
conditions in starting railway trains or commercial motor vehicles and 
in working the latter in deep snow, mud, or sand. 

3. The high rotative speed when the resistance to be overcome is 
unfavorable thereto. Turbine pumps in successive stages have arisen 
to remove this difficulty, but air and gas compressing under high pres- 
sures, the rolling mill, the mine-hoist, and the factory transmitting power 
by mechanical means must be operated by the slower moving recipro- 
cating engine or objectionable reducing gears must be introduced. In 
marine conditions, the small screw at high speed lacks holding power by 
reason of its reduced area. 

4. The stored energy in the mass of the rotor revolving at high speed 
with low friction. This makes the stopping of the main shaft a slow 
process requiring many minutes, and in case of accident or emergency 
a quick stop often becomes imperative. In electric drives, the opening 
of the switch may accomplish all that is required; in mechanical drives, 
a clutch may be interposed between motor and transmission and be 
thrown out by power. But a brake or the use of a reverse turbine as 
such will be required if the rotor itself is to be stopped. In marine 
practice this slow arrest of the screw invades promptness of response 
to manoeuvering orders. 

5. The economy drops with lowered speed below that for which the 
machine is designed. 



538 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

6. The conditions of running cannot be changed respecting speed or 
initial or final pressures without affecting economy and efficiency. 

7. Fluid friction of water in the steam retards speed. 

8. High-speed turbines have a tendency to hum. This is partly 
nozzle and blade noise, having a likelihood of reaching a musical note 
or tone which the air will transmit. Or the noise is from the generator. 
This air vibration is different from the vibration of foundations or solid 
masses, and can be checked by use of double doors and windows. Gen- 
erator hum is lessened by inclosing this also and sending a forced 
circulation of air within the casing. 

9. The wear of the blades by erosion, due probably to water and its 
mechanical action in condensation during expansion, replaces the wear 
of pistons and cylinders in the other type. Water backing up from 
jet condensers into the lower stage has also made trouble from brake- 
action and breakage of blades which were not strong enough to with- 
stand impact against solid water in a mass. 

10. Breakage of a blade usually destroys many others before it 
becomes comminuted and gets out of the way. 

11. The turbine shares the peculiarity of all high-speed machinery 
that when anything goes wrong in its lubrication the harm comes very 
quickly. While there is less to oversee and do about the turbine than 
in the reciprocating engine, yet the greatest care is required to see that 
steps and bearings are in good condition and to keep all apparatus in 
prime condition. 

359. Costs of the Steam Turbine. The question of the cost of the 
turbine appears in the usual two forms. The first is the purchase cost 
and the second is the cost of operating. As the question always appears 
as a competitive one as respects a reciprocating engine of the same 
capacity, a type must be chosen for each alternative. The first cost of 
the cheaper to build will not come down much below the standard 
of the more expensive to make so long as competition exists. 

To assume a set of conditions, let a 1000-horsepower unit be selected, 
with a 750-kilowatt generator. The turbine has no indicated horse- 
power properly so called, so that the electrical output must be its stand- 
ard. If the steam pressure be called 150 pounds, a cross-compound 
of 24 and 50 inch cylinders and 42-inch stroke at 100 revolutions should 
give 1200 horsepower to allow for loss and possible overload. Assume 
the generator to be of 2300- volt capacity, alternating, 3-phase, 60-cycle. 

The turbine and generator together at $30 per kilowatt would cost 
$22,500. The engine alone at $20 per kilowatt will cost $15,000 or a little 
less; the generator a little less than $9000. Each will require an exciter 
at $1500 with its own engine. 



THE STEAM-TURBINE 



539 



The turbine condenser will probably be made of surface type for 
safety. If 4 square feet be allowed per kilowatt, there will be 3000 
square feet of tube area, and the cooling water will be 60 to 70 pounds 
per pound of steam. Independent steam-driven centrifugal circulating 
pump will probably be chosen with 12-inch area driven by an 8 X 8 
inch engine, and an independent air-pump steam driven. Condenser 
and pumps amount to $5200. For the reciprocating engine the con- 
denser can be smaller, with 35 pounds of water per square foot of cooling 
surface and 10 pounds of steam condensed per hour per square foot. 
A direct-acting circulating and air-pump steam driven can be used with 
such a surface condenser, making the total cost $3000. If a siphon or 
barometric condenser is selected, requiring from 40 to 50 pounds of 
water per pound of steam, the cost falls to $2500 for the reciprocating 
engine and to $4000 for the turbine. The latter will need 60 times the 
weight of the steam it condenses. A simple jet condenser for the 
engine would cost $2000. An allowance of $200 should be made for 
erecting the turbine condenser. 

The foundation cost is greatly in favor of the turbine. If made of 
the same depth, say 12 feet, and at a cost of $6 per cubic yard, the tur- 
bine foundation of 40 cubic yards of concrete will be $250 and the 
engine foundation of 276 cubic yards will be $1656. 

The turbine will have a superheater, say for 100 degrees. The cost 
of the superheater is at $2 per boiler horsepower for 50 degrees and 
$2.60 for 100 degrees. If the turbine uses less than 16 pounds of water 
per horsepower per hour, 500 boiler horsepower should be enough 
(paragraf 10). Hence the superheater will cost $1300. An excess of 
freight and erection charges for the engine and generator should come 
to $2500. Summarizing: 

TABLE XVII. 

COMPARATIVE INSTALLATION COSTS OF TURBINE AND ENGINE. 



Item. 



Engine 

Generator 

Condenser surface. 

Foundations 

Superheater 

Erections 



Reciprocating Engine. 



$15,000 
9,000 
3,000 
1,656 



2,300 



$30,956 



Turbine. 



$22,500 

5,200 

250 

1,300 



$29,250 



H 



540 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

That is, the engine plant costs a Httle over $40 per kilowatt and the 
turbine plant a little over $38. In larger turbine units, and by omitting 
the superheater and modifying other details, the price per kilowatt in 
3000 units is about $20. 

The saving in cost of land and buildings is very considerable for the 
turbine. The turbine-room assumed at one-half the floor area of the 
engine-room will give a material reduction of cost when land is dear. 
The engine-room would have an area of 7600 square feet in the above 
plant, and the turbine of 3600 square feet floor space saves 4000 square 
feet. 

With respect to operating cost, the standard report of recent research 
is from the plant of the subway electric power station in New York 
City."^ The data of the first column are from a year's record of costs in 
the plant. The others are from costs obtained elsewhere, reduced to 
the conditions to which the first column applies. 



TABLE XVIII. 

CHARGES PER KILOWATT-HOUR FOR POWER-PLANT MAINTENANCE AND 

OPERATION. 



Item. 


Reciprocating 
Engines. 


Steam Turbines. 


Reciprocating 

Engines and 

Steam Turbines. 


1 


2 


3 


4 


MAINTENANCE. 

1. Engine-room 

2. Boiler-room 

3. Coal and ash handling 

4. Electrical machinery 

OPERATION. 

5. Labor, coal and ash 

6. Removal of ashes 


2.57 
4.61 
0.58 
1.12 

2.26 
1.06 
0.74 
7.15 
0.17 
61.30 
7.14 
6.71 
1.77 
0.30 
2.52 


0.51 
4.30 
0.54 
1.12 

2.11 
0.94 
0.74 
6.68 
0.17 
57.30 
0.71 
1.35 
0.35 
0.30 
2.52 


1.54 
3.52 
0.44 
1.12 

1.74 
0.80 


7. Rental of dock 


0.74 


8. Labor, boiler-room 


5.46 


9. Supplies, boiler-room 

10. Coal, boiler-room 


0.17 
46.87 


11. Water 


5.46 


12. Labor, engine-room 

13. Lubrication 


4.03 
1.01 


14. Supplies, engine-room 

15. Labor, electrical 


0.30 
2.52 






16. Relative cost of operation 

and maintenance 

17. Relative investment cost 

in percentage 


100.00 
100.00 


79.64 
82.50 


75.72 
77.00 



* Henry G. Stott, 
January, 1906. 



Power Plant Economics." Trans. Amer Inst Elec. Engrs. 



THE STEAM-TURBINE 



541 



360. Performance of the Steam Turbine. Great care should be 
exercised in generalizing from comparative tests of turbines with recip- 
rocating engines. The reciprocating engine has a most economical load 
at which it may be run; the turbine runs with essentially the same 
economy over a wide range from below its normal load to a considerable 
overload — even as high as 150 per cent. The turbine is also usually 
helped by its more recent installation and with higher pressures, super- 
heat, and better vacuum conditions to favor it than the older recip- 




'12 13 14 . 15 16 17 18 19 ^ 

Pounds Steam per Electrical Horse Power per Hour 

Fig. 486. 



rocating engines. Under steady loads, the reciprocating engine at its 
best speeds will show a little better economy than the turbine. Under 
average conditions, the average high-grade reciprocating engine has 
the same economy as the average turbine. Fig. 486 shows plotted 
comparisons showing the water rate with underload, best load, and 
overload of three types. When builders are allowed to fix their own 
conditions and test in their own shops, the water rate will run from 
14.5 down to 12.25 in sizes from 1500 kilowatts up to 3000 kilowatts. 



542 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

Fig. 487 shows results of tests under varying conditions. The Curtis 
marine guarantee is for 14 pounds at 21 knots, and 23.1 pounds at 
10 knots speed. 

From the absence of alternations of temperature the turbine suffers 
less from internal condensation than the reciprocating engine; con- 
sequently the meaning of high superheat is not so great. The gain 
from it is rather a mechanical action in diminishing fluid friction among 
the blades than the thermal advantages it offers in the other type. 
Care must be taken not to let any excess of temperature get past the 



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lower wheel unreduced by doing work, since its effect will be to increase 
the weight of condensing water or else to impair the vacuum. The 
turbine is exceedingly sensitive to the excellence of the vacuum. 

361. Concluding Comment. The demand for the steam turbine and 
its success in meeting it are the outcome of the growth and development 
of the electrical transmission of energy in the form of light and power. 
The electrical generator has called for high speed; the turbine is at its 
best under these conditions. The economy of the steam turbine and 
its conveniences (paragraf 357) have called for its appHcation to other 
functions than driving generators, and high-speed rotary machinery has 
been developed to meet the attributes of the turbine. It is safe to say, 



THE STEAM-TURBINE 543 

therefore, that more and more the turbine will take on itself the work 
heretofore done by the reciprocating engine, or as a supplement thereto 
(paragraf 355). This means that the turbine marks a stage in the 
development of the heat-power plant of importance analogous to that 
of the separate condenser, the principle of continuous expansion, the 
automatically controlled cut-off, and the economy of superheat. Where 
the speed is constant and high; where rotary machinery is applicable; 
where the resistance varies with the speed from zero at starting to the 
full load, the turbine has the field of the future, and will be rivalled in it 
only by the internal combustion motor. At first such motor will be 
reciprocating; if later knowledge of the laws of expansion should reveal 
some way of applying such expansion of hot gases to driving a gas tur- 
bine, this latter will again supplant the reciprocating or piston internal 
combustion motor. Hence the steam turbine has the electric power 
and lighting central station, electric lighting of trains and vessels and 
isolated plants; it has the high-speed passenger and naval cruiser service, 
the yacht and launch, the rotary blowing and pumping motor service. 
Most factories of the future will use electrical transmission of their 
power, with all the conveniences of that system. 

The field least open to the turbine or closed to it is that where the 
maximum resistance has to be overcome in starting from rest, or at 
very low speeds of the motor machine. That is, the requirement of 
maximum starting moment or torque with diminishing intensity of 
effort per unit of time as the speed increases is that which the method 
of utilizing expansion in the reciprocating engine is best adapted to 
meet and the turbine least adapted for. These appear in the loco- 
motive attached to a heavy train and the commercial motor- vehicle; 
in high-pressure pumping of large masses of liquid or against the resist- 
ance of long pipes; in compression of gases or air; in the side-wheel or 
paddle-wheel engine, the metal-working rolling mill, the hydrauhc 
transmission of power or high-pressure fire-service for cities, in the 
freighter or towing service at sea or on inland waters. The reciprocating 
engine of good construction and high economy already installed will not 
be displaced until worn out many years hence. The reciprocating engine 
therefore retains and will retain sufficient importance to justify the 
further and exhaustive study of its constructive details, valve gearing 
and governing. The first step in logical sequence will be the foundation 
and bed-plate of a typical reciprocating engine, to whose study the treat- 
ment now returns. 



CHAPTER XXI. 

ENGINE FOUNDATION AND BED-PLATE. 

365. Introductory. It must be obvious that when a piston is moved 
back and forth in the cylinder of a reciprocating engine under a pressure 
from expanding steam, the pressure upon the cylinder head is equal to 
that upon the moving piston. When the latter tends to move forward 
the cylinder has an equal tendency to slide backward. If the crank is 
to be moved by the piston, the cylinder must therefore be held stationary. 
It is important that the shaft of the engine be prevented from any other 
motion than its rotation in the bearings. The push and pull of the 
connecting-rod must be constrained so as to be in the desired directions 
only, to prevent wear, noise, heating, and lost work. Kinematically the 
engine being a four-link chain, one of these links must be anchored to 
something fixed, in order to render definite the motions of the other 
three. These conditions require that the cylinder guides and shaft 
bearings be so bound together, that the forces at play shall riot produce 
any undesired motions of the parts, nor cause shocks, jar, or vibrations 
to the machinery or building of which the motor engine is an element. 
The fixed link of the mechanism, or the connecting and unifying part 
of an engine to which its elements will be attached to keep them together 
and in line, will be called the bed-plate or bed, in stationary horizontal 
engine practice. In locomotive and vertical engines it is usually called 
the frame; in beam-engines for marine work, the lower element of the 
bed or frame is often called the sole-plate. 

The bed-plate or frame should make the engine self-contained and 
capable of being erected anywhere where its weight can be adequately 
supported. This is measurably true of small and medium-sized engines 
where some attention has been paid to balancing. In the general case, 
however, it is not convenient to give to the bed-plate the mass necessary 
to withstand completely the shaking forces released in the engine when 
at work; in large engines the bed cannot be made rigid enough of itself 
to keep perfect alinement if the support below it is inadequate. Hence 
for both of these reasons it is customary to put the engine bed upon a 
masonry or concrete foundation, so that mass and support and aline- 
ment shall be furnished by it. Masonry and concrete give a mass 
absorbent of vibration and easily constructed in place. The foundation 

544 



ENGINE FOUNDATION AND BED-PLATE 545 

can go down below the frost-line, and is not liable to destruction below 
ground. Cast-iron surfaces, or sub-bed-plates, are designed with certain 
light and high-speed engines to lift the engine above floor-levels and 
enable small fly-wheels to turn clear of the top of the foundation. The 
bed-plate will be securely bolted to the foundation to make them one 
and compel them to act together in resisting shaking and vibration. 
How shall the desired mass of foundation be computed or arrived at? 
The foundation must resist motion laterally and up and down from the 
engine forces within it, or the pull of belts or transmission apparatus; 
it must support the static weight without tendency to unequal settling 
in the soil or ground on which it rests. 

366. Mechanics of the Engine Foundation. Shaliing Forces. The 
treatment of Chapter XV and paragrafs 259 to 263 requires to be 
extended when the engine is to be conceived as suspended from above 
by flexible cords with springs to carry its weight, and therefore free to 
move vertically or horizontally under the action of the forces at work 
within its own construction. The foundation is to take the place of the 
free suspension and resist any stresses which cannot be otherwise pro- 
vided for by a balance of forces in the engine itself. The foundation 
discussion therefore opens up the dynamics of the engine masses in 
both the plane of the cylinder axis and at right angles thereto. In the 
former discussion only the inertia effects parallel to the cylinder axis 
were computed, and with respect to their effects upon the turning 
moment at the crank-pin: it may be that the effort to balance effects 
of mass and inertia will result unfavorably to the turning moment. 
The designer must decide which set of conditions is to be paramount. 
In the locomotive, the motor-vehicle, and the marine engine, the balance 
is so much the most important that it must receive first place whatever 
the effect on the turning effort at the crank-pin; in high and medium- 
speed engines of stationary practice there is usually a compromise with 
the balance partial but not complete, and in the horizontal plane where 
such balance is the most important. In very slow engines it can be 
disregarded, although the engine wears longer when attention is paid 
to exact design. 

When the steam enters the cylinder behind the piston, it exerts a 
pressure PA upon the piston and the cylinder head. It has been made 
clear from paragrafs 260 to 263 that this effort does not reach the crank- 
pin and hence the bearing of the shaft, after motion of the piston begins,, 
until the masses attached to the pin have been accelerated at or near 
half-stroke. Hence the piston head is forced away from the crank- 
shaft by the force PA with the mass of the reciprocating parts as its 
abutment during the acceleration; and during the retardation in the 



546 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

second half of the stroke the crank-shaft is being forced in the other 
direction by such stored Hving force given out upon the pin and shaft. 
The mass of the piston cross-sections and the cross-sections of rods and 
pins are all fixed primarily by the metal necessary to resist the inten- 
sity of PA; the mass due to this computation adds the value of the 
inertia stresses which these same materials and elements must resist. 
Hence it would appear that the stresses would fall into four groups: 

1. Those imposed from without from the intensity of PA. 

2. Those resulting within from PA and resulting centrifugal accel- 
erations due to the speed. These two give the masses in action. 

3. The turning moment of the crank-pin where these impressed 
forces pass effectively to their external work. 

4. Unbalanced or balanced forces which do not get away to do 
industrial work at crank-pin or crank-shaft, but must be cared for in the 
foundation. 

These last are the shaking forces. They arise from two origins: 

1. Unbalanced forces and moments due to the reciprocating parts. 

2. Unbalanced moments and forces due to the rotating parts. In- 
equality of the turning effort due both to the varying cylinder pressure 
and angular velocity of the fly-wheel and crank will be factors in this, or 
inequahties due to defective adjustment of the governing function to 
the resistance, or wide or sudden variations in such resistance as related 
to the stored energy of the fly-wheel. It would appear therefore that 
reciprocating balance can only be partly attained by a rotating mass, 
as is usually the practice, and that under variation of load and speed 
the balancing masses will disturb a previously existing rotating balance. 

The theoretical condition for an equilibrium or balance around an axis of revolution 
is twofold. First, the algebraic sum of all moments revolving in the same plane 
around the axis of revolution shall be zero. If not, there will be another axis in space 
where they will be zero, and the system will press bodily or jump the shaft and 
weights to get into this axis. Mathematically, if W be the weight of each mass and 
R its distance from the center of the shaft, then S WR = 0. Secondly, if, as is the 
usual case, these weights or masses are not in one plane, the shaft will have a tendency 
to flex or bend, until the condition is reached that the algebraic sum of the moments 
2 WR, when multiplied by a lever-arm y measuring the distance of the plane of 
rotation of each weight from a plane at right angles to the axis of rotation, shall also 
have an algebraic sum of zero, or S WRy = 0. The first condition gives a standing 
balance; the second gives a running balance. 

Four differing sets of conditions will present themselves — the horizontal single 
and multi-cylinder engine: the vertical single and multi -cylinder engine. 

In the single horizontal engine, the pressure PA at the dead-center is resisted by 
the main bearing and the cylinder head, which are in equilibrium. The intensity of 
this may usually be made secondary to that of the inertia effect of the reciprocating 



ENGINE FOUNDATION AND BED-PLATE 547 

parts. This was shown in paragraf 260 to be for each square inch of piston area to be 

p = 0.00034 wRN\ 
or for the entire weight of the reciprocating masses 

P = 0.00034 WRm 

when the obliquity of the connecting-rod is neglected or it is regarded as of infinite 
length. 

Hence a balance weight TF^ in the plane of the crank-pin, opposite to the application 
of the reciprocating weight treated as a revolving weight and with a radius r^ from 
the center of the shaft, would be 

0.00034 WRm = 0.00034 W^r^N^, 

whence 

It is not quite fair to consider the whole weight of the connecting-rod as recipro- 
cating; the conventional allotment is to take one-half as rotating and one-half 
reciprocating. Then the value for S W being found, their centrifugal moment 
about a plane parallel to the rotation of the crank-pin is made zero, to prevent a 
bending of the crank and pin or shaft. If this last were not done, there would be a 
tendency for the engine to shake sidewise and move laterally on its foundation at the 
end away from the crank — a revolution around a vertical axis at right angles to the 
shaft. Two horizontal cylinders side by side as in the cross-compound could be 
balanced with cranks at ISC except for the obliquity of the connecting-rod. With 
cranks at 90° the tendency to rotate horizontally around the vertical axis through 
the horizontal shaft reappears. The four-cylinder engine can be perfectly balanced, 
except for the small error of the connecting-rods. The only connecting-rod engine 
perfectly balanced is the type of Fig. 490, known in America as the Wells engine and 
in England as Barker's, in which the upper cylinder has two piston-rods and con- 
necting-rods and the lower one has one. These act on crank-pins at 180° apart, and 
by proportioning their weights and masses both the pressure values and inertia forces 
are in equilibrium at all times less only variations in the expansion in the high-pressure 
cylinder. Three-cylinder engines with equal reciprocating masses and rotating 
moments are also in balance except for the twisting tendency to rock around an axis 
at right angles to the shaft. 

It is a great advantage of the center-crank engine that the counterweight to 
balance the reciprocating mass when divided between the two cranks becomes 
symmetrical respecting the vertical axis through the shaft, and steadies the cylinder 
end from its tendency to sling. 

But it is evident that by introducing the revolving counterweight to steady the 
engine from horizontal shaking the unbalanced revolving weight is going to produce 
shaking vertically. To attempt to balance the counterweight is to unbalance the 
reciprocating mass again. Hence the foundation becomes inevitable if the horizontal 
engine is to be balanced horizontally, so that foundation bolts can hold the bed 
down. In vertical engines, the balance in a horizontal plane or at right angles to the 
cylinder axis is the important one, so that equality of turning moment is usually 
sacrificed in practice. 

In vertical engines with two cylinders side by side, the tendency with quartering 
cranks is to rock or swing about the edge of the bed-plate at right angles to the 



548 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




DESCRIPTION. 

A — The high pressure cylinder. 

B— The low pressure cylinder. 

C— The steam chest. 

D — The receiver. 

E— The exhaust passage, 

a— The high-pressure piston. 

b— The low pressure piston. 

c— The piston valve. 

d-The valve casing. 

e— The reversing lever. 

F— Crank-shaft. 




Fig. 490. 



ENGINE FOUNDATION AND BED-PLATE 549 

shaft. The four-cylinder side-by-side balances again, and the three-cylinder type 
except for the tendency of the cylinders to oscillate. The initial pressure also is 
effective to shake in vertical engines. 

In the locomotive and the motor car where there can be no foundation, the prac- 
tice has been to balance about two-thirds of the reciprocating or centrifugal weight 
and let the counterweight produce its effect downward upon the track and upward 
upon the mass of the engine or motor with the springs as absorbers between. The 
side swinging of the locomotive, called wig-wagging or elbowing, is much the most 
objectionable, as it causes jerks upon the traction or draw bars and makes the engine 
liable to derailment. Any tendency of the cylinders to lift is also dangerous, par- 
ticularly on curves. Locomotive balancing also includes a balance for the effect of 
the reciprocating parts on the other side of the engine, at 90° from the one under 
observation, and the further factor that the counterweight being in the driving-wheel 
Hself must move through space at twice the velocity of the engine itself or of the 
reciprocating parts when the counterweight is at the top of the wheel. The parallel 
or coupling rods also have to be allowed for in the computations for balance. 

In computing the shaking forces, which can be done either analytically or graphi- 
cally, it will be plain that the interest of the designer is upon the axial components 
parallel to the axis of the cylinder and those transverse or at right angles to them. 
The reciprocating masses act axially, and will be equal to a force 0.00034 WN^R, 
The centrifugal components will be decomposable into two at right angles for each 
crank angle d, giving the axial component 0.00034 WN^R cos d and the transverse 
0.00034 WN^R sin d. These should be added together when both are in action, 
giving a resultant in a curve on a straight line base. 

A rough practical rule has been to give to the foundation a weight 
at least ten times the value of the impinging force which it is to resist. 
This is a practice based upon giving to an anvil ten times the mass of 
the hammer head delivering blows upon it. In applying it the plan 
has been: 

First, to have the foundation deep enough to raise the engine cylinder 
axis to the desired level above the engine-room floor. 

Second, to have it go deep enough into the ground or far enough 
below the surface to be beyond the effects which cause unequal setthng 
either from frost, vibrations, or the influence of loads borne by adjacent 
ground. The depth below the surface desirable for an engine-founda- 
tion will vary, but it is rarely safe to permit less than three feet of foun- 
dation below the general level. In excessive cold and in exposed sit- 
uations the effect of frost will be felt down to six feet below the general 
level. 

Third, the engine-foundation must furnish sufficient mass to absorb 
vibration if the bed-plate is not massive enough to do it alone. The 
foundation being made up of masonry is easily and conveniently built 
up in place, while to make a massive casting would not only be more 
costly per cubic foot, but would make weights of such magnitude that 
handling would be troublesome. 



550 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

When the foundation rests on rock and is not sufficiently massive 
it has been found that the vibrations caused by reactions in the engine 
are transmitted almost perfectly to the adjoining foundation upon the 
same rock. Great care has to be observed to attain success. 

Fourth, the foundation must have area enough to support the con- 
centrated weight of the engine upon the ground by distributing that 
weight over a sufficient area to prevent settling. Accepted figures for 
the supporting power of different soils are given in the following table: 
Alluvial soil from .5 to 1 ton per square foot. 



Clay, soft .... 

" dry 

" thick . . . 

Sand, clean dry 
" compact 



1 " 1.5 

2 " 4: 

4 " 6 
2 " 4 

4: " S 

Gravel and coarses and, from 4 to 8 tons per square foot if 

protected from water. 
Hard rock, up to 200 tons per square foot in thick strata. 

If the soil is so unreliable as to require piling, crib work, and other 
artificial underpinning, the student is referred to text-books which 
make a specialty of foundations. 

Then if when these requirements have been met the weight or mass 
is less than one-tenth of the force per stroke due to the skaking effort, 
the necessary additional mass is added in depth and the other dimen-» 
sions to make it so. 

367. Construction of Engine-foundations. The foundation for very 
large engines will be of cut or dressed masonry according to the usual 
specifications for first-class masonry. Where the importance of the 
structure warrants it, tunnels or thoroughfares will be made or left 
through the mass of the foundation by which access may be had to the 
lower ends of the bolts by which the bed-plate is bolted to the masonry 
(Fig. 491). 

For small engines, footings of rough masonry or ashlar may be used 
to distribute the pressure, and on this footing the foundation proper of 
brick will be built. The third plan is to make the foundation a monolith 
of concrete. Upon a proper footing to distribute the weight, a box of 
rough boards without top or bottom is laid, and within it successive 
layers of cement concrete are thrown in and well rammed until the 
desired height is reached. When brick is used it should be of first quality, 
hard-burned, and laid in cement-mortar. Common lime-mortar is Uable 
to crumble and disintegrate under vibration, and the whole principle of 
the foundation is to have it act as a solid mass. When appearance is to 
be considered, the face of the brick foundation may be made of face or 



ENGINE FOUNDATION AND BED-PLATE 



551 




552 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

pressed brick, while the interior is of ordinary grades. Since the bed- 
plate is to be bolted to the foundation, the greatest care must be observed 
in locating the necessary bolts in their proper places. 

368. Footings to Prevent Vibration. The mass which it is convenient 
to get in a vertical engine bed-plate is often not enough to provide for the 
absorption of all vibration. The vertical engine, when chosen because 
floor-space is to be saved, does not call for extended area in the founda- 
tion, so that sufficient mass can only be gotten by going deep. Where 
this is inconvenient, or where rock is struck, engineers have had to 
provide special footings to arrest vibration. It has been tried by some 
to underlay the foundation proper with timber or rubber, but a springing 
material of a class to which these belong is often the occasion which 
causes the very difficulties they are designed to prevent. 

Vibration of machinery or any solid substance is of two sorts: the 
material either swings crosswise as in the vibrating string of a musical 
instrument or in a flapping belt, or the motion of the particles is length- 
wise or parallel to their long axis. If the oscillation or vibrating period 
of the material used as an absorber of vibration happens to coincide with 
the vibration period caused in the engine-frame by the speed of recipro- 
cation or by the belt-flap, the deadener partakes, and multiplies the 
objectionable vibration. What is to be sought to deaden vibration and 
arrest its transmission is some material to underlie the foundation which 
shall be without any resihence whatever. 

Probably no better material is to be found for the purpose of stopping 
vibration than sand, if it can be kept dry and all motion prevented, and 
the foundation-block itself is of sufficient mass. The foundation-pit is 
dug two or three feet deeper and two or three feet wider on all sides than 
the foundation proper is to be. This pit is surrounded with proper 
sheathing to prevent the displacement of the sand, which is filled in 
two or three feet below the bottom of the foundation, and then around it 
on the sides as it is built up. Hair-felt or mineral-wool layers have been 
used underneath the footing-course. If the foundation-block is not 
massive enough, these methods or expedients only aggravate the diffi- 
culty which they are intended to cure. Very satisfactory results have 
been obtained abroad from the use of asphaltic concrete for massive 
foundations. It possesses a certain sort of elasticity with its massive 
character, and its period of vibration is so definite and so much shorter 
than the period of the engine's vibrations that the latter are broken up 
and neutralized before they reach the transmitting rock or hard-pan. 

If any part of the engine bed or frame be flexible from its construction 
or from the slacking off of bolts, a possible vibration of the frame itself 
may take place, due to its elasticity and the modulus of the material. 



ENGINE FOUNDATION AND BED-PLATE 



553 




Fig. 492. 




Fig. 493. 



554 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

Stiff frames with a very short natural vibration period are better than 
simpler ones of a longer period, since the possible synchronizing of the 
reciprocation period with that of the vibrating bed would make danger- 
ous and impossible stresses. 

Most annoying vibrations are caused in high-speed engines by the 
impact of steam in an exhaust-pipe with elbows. The difficulty is 
intensified when there are water or oil drops in the exhaust current. 
Their impact against the elbow which deflects them will set lengths of 
pipe atremble, and their motion will be transmitted over a very extensive 
area. 

369. Foundation-bolts. The bed-plate requires to be strongly and 
stiffly secured to the foundation in order that the latter may act with 
the bed-plate as one mass, and to prevent the bed-plate from moving 
upon the foundation. These bolts will vary in size with the size of the 
engine, but it is very undesirable to use bolts of such small diameter that 
it can be possible to twist them off with any ordinary wrench. Common 
diameters of bolts for engines of medium size would be from 1| to H 
inches diameter. The largest engines will require 2-inch bolts, but the 
smallest would use |-inch. The length of these bolts will be determined 
by convenience. It is desirable to have them go a good way down into 
the foundation, if not all the way to the bottom, in order that the 
upward strain upon them may be widely distributed in the foundation. 

The location of these bolts in the foundation must be determined by 
the holes in the bed-plate through which they have to pass. It will be 
seen by examining typical bed-plates that as a general rule there are 
bolts at the cylinder end, or in the feet, and bolts at the crank-shaft end 
(Figs. 491 and 493). The bolts, furthermore, have to be built into the 
foundation, and at such a height that when the foundation is completed, 
and the bed-plate placed upon it, the upper end of the bolts shall pro- 
trude through the holes in the bed-plate enough to take the nut which 
these upper ends are to carry. 

The method used to secure this object is shown in Figs. 492 and 493, 
which present a typical arrangement for this purpose. The wooden 
frame is called a template. It has holes made through it at points 
which correspond to the holes in the bed-plate, and when the nuts are 
in place on the upper end of the bolts the template is adjusted to 
the proper height above the datum plane, or plane of reference, and the 
foundation is built around the hanging bolts. The lower ends of the 
bolts are fitted with thread and nuts, on top of which rest the bearing 
or distributing plates or washers of cast or wrought iron. The dis- 
tributing-plate is to enable the effort of the bolt to be borne by a number 
of bricks without danger of pulHng through, and the nut and thread 



ENGINE FOUNDATION AND BED-PLATE 555 

permit a vertical adjustment of the bearing-plate so that it shall come 
at the under surface of a joint in the coursed masonry. To permit of a 
certain limited horizontal adjustment of these foundation-bolts, several 
builders have surrounded the bolts with a length of pipe or a hollow 
wooden box making a round or square tube reaching from the bearing- 
plate to the top of the masonry. The diameter of this pipe is so chosen 
that the bolt can be deflected within the hole which the pipe makes, 
and, after the bolt is in place and the alinement completed, the space 
between the bolt and the pipe is filled with cement and the position of 
the bolt is fixed. The template in Figs. 492 and 493 shows the bolts 
required for the outer bearing of the engine-shaft attached to the prin- 
cipal template. This is usual when drawings of the template are fur- 
nished by the engine-builder and it is desired to make the foundation all 
in one piece. Where the length of the engine-shaft makes it desirable 
to have a separate foundation for this outer bearing it is usually more 
convenient to work with an independent template. 

370. Alinement of Foundation-template. The foundation-bolts of 
the bed-plate will bear a certain relation to the axis of the cylinder. 
The axis of the cylinder should be in a plane truly at right angles with 
the axis of the engine-shaft. If the engine-shaft is to drive a line-shaft 
by belting or gearing, these two shafts should be truly parallel. Hence 
it is of prime importance to have the cylinder-axis perpendicular to 
the line of shafting, and the template which carries the bolts must be 
very carefully placed or squared with respect to these determining 
lines. The drawing furnished by the builder of the engine from which 
the template is to be made usually has on it the center-fine of the cylin- 
der, so that it can be laid out upon the boards of the template. 

For the obtaining of the vertical plane through the cylinder-axis a 
line stretched over the foundation-pit and carried to suspended plumb- 
bobs is the usual device. For laying off the center-line of shafting or 
wall-lines the expedient of snapping a chalk-line upon the floor is the 
most convenient. The centers of the shaft are transferred to the floor 
by plumb-lines, or offsets may be taken from permanent walls. Such 
center-lines having been established, the plane at right angles to each is 
established by points and lines, using either a transit with graduated 
horizontal limb and making repeated readings, or by the ordinary 
geometric methods, or by the use of a massive T square whose head 
and blade exceed six feet in length and whose squareness has been 
carefully verified. 

If a pulley or belt-wheel has been placed upon the line-shaft to which 
it is desired to draw a perpendicular line, a most convenient method is to 
stretch a twine or fine wire across the diameter of the pulley as nearly as 



556 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

the shaft will permit. With pulleys which have been turned, the edges 
of the face determine a plane perpendicular to the axis, so that the tense 
string touching the face at one point will only touch the face at a point 
on the other side of the shaft when the further end of the string lies in a 
plane which is perpendicular to the axis. This same method is a very 
convenient one to extend for the purpose of bringing two shafts parallel 
to each other where both carry pulleys, but is only applicable for either 
use where both pulleys are so fitted as to run perfectly true when the 
shafts revolve. It is one of the prime advantages of the system of 
electrical transmission of power that such care in alining the engine is 
of no importance. 

371. Locating the Bed-plate on the Foundation. The foundation 
being completed, the bed-plate is to be lifted upon it and lowered into 
place with the bolts passing up through the holes in the bed-plate. 




Tig 494. 



Where cranes or similar lifting appliances are a feature of the power- 
house equipment this process becomes simple. In their absence the bed- 
plate must be lifted by jacks and blocking high enough to clear the bolts. 
It must then be rolled on skids into place, and then lowered by the suc- 
cessive withdrawing of the blocking. 

The masons or bricklayers who have built the foundation do not 
usually have appliances for working to as close dimensions or as accurate 
levels as the setting of the engine requires. Furthermore, the top of 
the foundation is rarely a true plane, while the bottom of the bed-plate 



ENGINE FOUNDATION AND BED-PLATE 557 

is very nearly a plane as a rule. It is necessary, therefore, to make a 
joint between the bed-plate and the masonry- work which shall support 
the bed-plate all over and in a plane as nearly level as it can be made. 
This process is so much easier when the brickwork or jointed masonry 
is covered by a single flat cap-stone, that where the dimensions of the 
foundation permit its use it will be preferred. It is usually a sawed or 
planed slab of bluestone or flagstone from four to six inches thick, 
and a little larger than the foundation-pier to which it serves as a finish 
or coping. The holes for the foundation-bolts have to be drilled in it, 
and it is lowered to its place upon a good bedding of cement. In thfe 
absence of such a cap or coping the bearing of the bed-plate comes 
upon a surface which is full of joints. The bed-plate is lowered over 
the foundation-bolts, and rests upon thin flat shims, or wedges of metal, 
which are placed on each side of the bolts between the bed-plate and the 
foundation. A, B, C, and D in Fig. 494 show such adjusting wedges. 
The nuts of the bolts are then screwed home, compressing the shims, 
while the bed-plate is carefully leveled as the strain is taken at each 
bolt. By driving in or loosening the shims any distortion or warping of 
the bed-plate by the bolts is prevented, and the bolts are tightened home 
until they refuse to go further. 

The bed-plate is now rigidly bolted to the foundation and rests upon a 
number of points in a plane. Between the bed-plate and the foundation 
is a place between the shims equal to their thickness, and this joint 
requires to be filled. The materials used for this purpose in setting a 
bed-plate and making the joint are five. They are methods applicable 
to the setting of any machinery. 

1. Shredded oakum may be driven into the joint with a chisel, as the 
seams of wooden vessels used to be calked. This makes an elastic sort 
of joint, but it lacks permanency. 

2. Felted hair is used in the same way and has the same properties. 

3. A rust-joint, as it is called, may be used. This is made by taking 
a thin cement-grout into which cast-iron borings or chips are intro- 
duced with a little powdered sal ammoniac and flour of sulphur. A 
dam of putty or clay is made around the outside of the bed-plate, and 
this mixture run into the joint and well worked in with a trowel. The 
rusting metal unites the mixture to the iron, and the cement to the 
stone. 

4. The sulphur-joint. This is one of the most widely used methods 
for bedding the engine. A clay or putty dam is made around the bed- 
plate, and the ordinary roll sulphur melted in an old kettle and poured 
into the joint between the bed and the masonry. It expands on solidi- 
fication somewhat Hke ice to fill every interstice and give full support 



558 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

to the bed-plate. It undergoes no deterioration from oil or vibration. 
If care is not taken in melting the sulphur, it will become too hot and 
begin to oxidize, giving off an irrespirable gas. Sulphur in melting 
becomes fluid at a comparatively low temperature, becomes more viscid 
as the temperature rises, and passes to a second fluidity just before it is 
ready to burn. 

5. The type-metal joint. Advantage is taken of the property 
possessed by certain antimony alloys (such as Babbitt, type-metal, etc.) 
of expanding at the moment of solidification, to use them for bedding or 
jointing bed-plates. The method of using them is the same as that 
practiced with sulphur, and they are preferred by many engineers par- 
ticularly for bedding the narrow feet used with Corliss bed-plates. 

373. Alinement of Outer Pillow-block or Shaft-bearing. In engines 
of the center-crank type (paragraf 290, Figs. 406, 408) the unit is 
self-contained, and all bearings are on the bed-plate itself. In the side- 
crank type (paragraf 289) only the bearing next to the crank is carried 
by the bed-plate and the bearing which is outside the generator or belt 
or fly-wheel and near the outer end of such shaft on the separated element 
of the foundations must be carefully adjusted. This care is necessary 
for the following reasons: 

If the outer bearing is too high or too low, it will force the crank to 
revolve in a plane making an angle with the true vertical plane, and 
twist the connecting-rod in each stroke. If out of place in a horizontal 
plane while correctly located in a vertical plane, it will force the crank 
to revolve in a plane which makes an angle with the axis of the cylinder, 
in which case it will bend the connecting-rod in each stroke; or it may 
be out of place in both planes, so that the connecting-rod will be both 
twisted and bent. The effect of either or both errors of alinement of 
this outer bearing is to wear the crank-pin out of its cylind^rical shape, 
and to cause a knock or pound, and heating at the joint, which no adjust- 
ment of these bearings will cure. The proper method of alining the 
outer bearing involves, first, the establishment of the true axis of the 
cylinder after the bed-plate is in place and the foundation- joint com- 
plete. This is best done by stretching a fine piano-wire through the 
empty cyhnder, carefully adjusting it to the center of the bore and 
fastening it tightly stretched to walls or fixed objects. To get the wire 
central is a matter of painstaking care and trial with gauges of wood or 
metal whose length is the cylinder-radius. The axis of the cylinder 
being established, the 'shaft and crank are put in place in the bearing on 
the bed while the outer bearing is provisionafly supported and located. 
The shaft is then turned until the crank coming towards its inner dead- 
center touches the wire which marks the prolongation of the cylinder- 



1 



ENGINE FOUNDATION AND BED-PLATE 



559 



axis. It will touch it at a certain distance from the end of the crank-pin 
and from one of its collars (Fig. 406). The shaft is then turned over 
until the crank-pin approaching its outer dead-center touches the wire. 
It will only touch it at an equal distance from its end or some fixed 
collar if the shaft is revolving around an axis truly at right angles to the 
wire. The outer bearing should be adjusted horizontally until the wire 
cuts the crank-pin at the same point and in the same plane on its outer 
and inner centers. 

The adjustment of the horizontal plane may be effected by a sensitive 
level if the engine has also been leveled in the plane at right angles to the 
cylinder-axis in setting upon the foundation. A more sensitive and 
satisfactory vertical adjustment of the outer bearing is made by putting 
the crank-pin at 90° from its dead-center, and holding a plumb-line so 
as to touch the wire at the pin, noting the distance of the vertical plane 
thus established from the end of the pin or a fixed collar. If the plumb- 
Une touching the wire also touches the crank-pin at the same distance 
from the reference-mark when the pin is at half-stroke below the wire, 
then the pin is turning in a vertical plane through the wire, and the outer 
bearing requires no vertical adjustment. 

Where adjustment is required the usual procedure is followed of 
correcting half the error and testing the alinement again. The outer 




Fig. 495. 



pillow-block is often made to rest upon a special foundation-plate which 
has provision for the adjustment upon it of the bearing proper in both 
the horizontal and vertical planes (Fig. 495). The vertical adjustment 
otherwise is made either by shimming or filling in with sulphur or type- 
metal below the plate, and the last and finest adjustment can be 
made by liners underneath the bearing-brasses. The alinement of 
vertical engines is usually simpler than that of horizontal engines, 
because the bearings are always on the bed-plate and have been made 
right as to ahnement by the builders in their shop-handling. The 



5G0 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

alinement in the erection of beam-engines is a simple and obvious 
extension of the principles laid down above. The vertical cylinder-axis 
and the vertical through the center of the crank-pin when the latter is 
at the top and at the bottom of its travel determine the vertical plane 
in which the beam must play, and the crank-pin at its 90° and 270° 
point must remain in that same plane. The alinement of engines 
afloat is so compHcated by the motion of the hull that little use can be 
made of perpendiculars and horizontals, and the center-lines must be 
depended on entirely. 

373. Forms of Engine Bed-plate. Horizontal Types. The bed-plate 
of a horizontal reciprocating engine appears in a comparatively few 
forms. The strains being the same in kind, differing only in intensity, 
the material to resist them will naturally be disposed in much the same 
way by different designers. Historically an early type is know^n as a 
tank or box bed-plate. It consists essentially of a box very much 
longer than it is wide, without top and often without bottom. The 
sides are made up of a combination of moldings, and the top of the 
sides is formed into wide flanges upon whose upper surface are bolted 
the cylinder and guides and the crank-bearing of the shaft. The space 
between the sides gives room for the motion of crank and connecting- 
rod. It doubtless received its name from the practice with .condensing 
engines of utilizing the area below the cylinder and -mechanism to 
accommodate the tanks used for the hot or the cold well (paragrafs 
508 and 515). Fig. 507 A in the Appendix shows a tank bed-plate of 
the ordinary type. It may also derive its name from its resemblance to 
a cast-iron trough. It usually has cross-ribs or girts to give it stiffness. 

Derived logically from the box or tank-bed is the one-piece bed or 
two-piece bed and sub-base type of Fig. 496, which shows three forms 
by different builders. The cyhnder casting is placed upon the end of 
the bed-plate instead of on the top, and is either cast in one piece with 
it, or bolted up. The one-piece method is open to the objection that a 
failure of any cylinder detail which necessitates a new cylinder casting 
necessarily compels a new bed-plate. The guides are either formed in 
the proper recess of the casting (middle and lower parts of Fig. 496) 
or are separately mounted as in the upper figure. The cyhnder and 
guides in the middle and lower system are bored by one bar so as to 
compel alinement. The cylinder is free to expand from the inner head 
without flexing itself or the bed, and the exhaust pipe leads away very 
directly. This form of bed is very usual for small and medium sized 
center-crank engines and lends itself easily to the side-crank type 
also by molding an addition or bolting it to the sub-base to carry the 
bearing for the outer pillow-block (lower detail of Fig. 496). This 



ENGINE FOUNDATION AND BED-PLATE 



561 




k. ■ ' . . 


»— "^^Si*.*" —1 ii':^^^E '^' 



Fig. 496. 



ENGINE FOUNDATION AND BED-PLATE 



563 



appendage can carry also the mountings for the pole pieces of the 
generator. The fundamental conception of this type of bed-plate 
was due to Mr. Charles T. Porter of America and was first largely used 
in England by Tangye. It is known by either name in the standard 
form* shown in Fig. 497, with the guides separately attached. The 
recent American modifications and developments of splash lubrication 
of the mechanism have developed the enclosed unit types of Fig. 496 
and the semi-enclosed of Fig. 498. 

For slower speed engines with longer crank-arm, longer cyhnder, and 
longer connecting-rod allowance, this form becomes too flexible without 




Fig. 498. 



a foot or support for the cylinder. Fig. 499 shows the type which will 
result for a belt drive with independent outboard bearing, masonry cap- 
stone, and an independent foot for the cylinder. This latter should 
enable the cylinder to go and come laterally by expansion by oval holes 
for the bolts which are vertical. 

A fifth type of bed-plate adapted only for long-stroke slow rotative 



564 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




I. 



I ' 






i 



ENGINE FOUNDATION AND BED-PLATE 



565 




566 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




Fig. 501. 



speed engines is designed so as to dispose of the metal required in a 
bed-plate more economically in the line of the stresses. It appears in 
many forms identified with the names of a number of various builders. 
That which is usually identified with the name of Corliss in America 
transforms the bed-plate into 
a brace between the two in- 
dependent castings of the 
crank-bearing and cylinder. 
Each of these has its own 
supporting foot or pedestal, 
and the bed is a casting 
bolted to each, and either 
not supported by any con- 
tact with the foundation or 
by a central foot only. This 
form of bed-plate is some- 
times called the girder bed- 
plate because the shape of the 
brace, in order to resist the 
strains upon it, becomes that 

of an I in both the vertical and in the horizontal plane. Fig. 500 repre- 
sents a standard bed-plate of this type, and Fig. 501 shows a section 
through the girder at the guides (see also other Corliss designs, 
Figs. 438, 504). 

The foundation plan of Fig. 493 is intended for an engine of this type 
of bed-plate, and shows the separate cap-stones. It has become recog- 
nized, however, more and more that economy of metal in the bed-plate 
offers no advantages except in marine, locomotive, or motor-vehicle 
practice. Hence the newer designs for heavy duty particularly have 
shown a return in even slow-speed types to the greater masses of the 
Porter and Tangye types, and make the guide-section of cylindrical or 
box type, with or without its own foot (Fig. 502) for the medium sizes 
or carry the sweeping curves of sohdity and grace pleasing to the eye as 
suggesting strength back to the cylinder head, with the guides supported 
as in Fig. 503. In the heaviest of all demands, for compound tandem 
rolling mill and street railway service the bed-plate will be carried solid 
at least to the first cylinder. Fig. 504, and the second one will have its 
own additional support, with a tie-piece to the first cylinder (Fig. 505). 
There are of course numberless modifications of the types which have 
been selected, each of which will be deserving of study, both as to the 
disposition of the weight of metal and the pleasure which they give to 
the eye as respects Une and proportion. A most interesting departure 



ENGINE FOUNDATION AND BED-PLATE 



567 




568 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

from conventional lines for a high-speed engine of light and medium 
power was the bed of the '' straight-line " engine of Fig. 506. This 
design carries the principle of permitted expansion to its logical end 
by having the crank-bearings tied to the cylinder by straight-line 
braces bolted to both^ but the cyhnder is not fastened to the foot which 
supports it^ but simply rests upon a bearing-surface. The engine can 
be designed to have all components downwards upon the pedestal in the 
absence of rigid connections, which removes the tendency to distort in 
expanding. The straight-line principle appears in many of the high- 
power heavy-duty types. 

374. The Bed or Frame of a Vertical Engine. It has been seen 
(paragrafs 273, 274) that the vertical engine has the cylinder almost 
always over the shaft. Hence the frame becomes a proper casting to 
carry the crank-shaft from which a suitable columnar structure shall 
arise to carry the weight of the cylinder and serve also to guide the 
cross-head. The general appearance of these columnar castings in the 
usual marine engine has given them the name of A frame (Figs. 389, 
391). In recent designs, to secure greater accessibility for the mechan- 
ism one side of such frames is made of hollow steel columns or rods, 
such as are fitted on the engine shown in Figs. 380, 381. Such engines 
are called open-front or open-side engines. Accessibility i^ a prime 
necessity of good design for vertical engines of this class, and is much 
better secured with such open frames. 

In beam-engines the bearing for the beam requires to be so designed 
as to keep satisfactory alinement. In early designs it will be found to 
resemble a massive column or pillar (Fig. 402A) ; in later engines a nearer 
approach has been made to the A frame or gallows-frame usual in river- 
boat practice. The gallows-frame in recent large engines is made of 
steel plate molded into box-girder shape and strongly braced. 

In the development of the construction of the typical engine the 
obvious detail to follow those of foundation and bed-plate should be 
the cylinder and its attachments. 



CHAPTER XXII. 

ENGINE CYLINDER, PISTON AND PISTON-ROD. 

375. The Cylinder Casting. The discussion in paragraf 259 of the 
stresses upon the elements of a typical engine should have made clear 
that overlying the computation of thickness for the walls to resist the 
stress PD by a balance of resistance 2 tf are such other stresses from 
water and from heat that the thickness of metal to be used in the 
cylinder is fixed rather on the basis of experience, by the condition of 
stiffness against deformation, and to be thick enough to permit of 
reboring when worn. 

The metal to be used for a cast-iron cylinder should be a uniform close- 
grained iron having a certain hardness or ability to resist abrasion. 
Experience in mixing irons in the foundry is of great use in this respect, 
and excellent results have been obtained from the use of an iron con- 
taining manganese. This metal seems to give a smooth or slippery 
surface to resist abrasion, while working easily under the pointed 
cutting-tools. The design of the cyHnder will be widely modified by 
the design of the valve-gear to be used and the type of valve chosen. 
In the horizontal engine the valve-chest for sliding fiat valves or piston 
valves will usually be at the side of the cylinder, or at the side and 
bottom if more than one valve is used. For rocking or oscillating valves 
of the Corliss type, the seats and chambers will be made in the heads. 
The valve-chest is rarely put on the top of the cylinder except in loco- 
motives. The reason for the preference for the side is the directness 
of the connection from engine-shaft to valve for driving itj while w^hen 
the valve is on top or out of the plane through the center of the shaft, 
the motion to the valve has to be indirect or by means of levers and 
rock-shaft. In vertical engines the valve can always be directly driven. 
Inspection is invited of the cylinder sections shown in Figs. 436 and 437 
for variations from the typical design selected as Fig. 510 to show certain 
features of construction. 

The casting of the cylinder is either made all in one piece with the 
massive bed-plate or it is bolted to.it. When made in one piece, as 
is usual in engines of the Tang3'e bed-plate pattern, a joint is avoided 
at the crank end of the cylinder, and no difficulty is to be experienced 
from the cylinder shifting its alinement with the bed. On the other 

569 



570 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

hand, the finishing of that end of the cyhnder is made more difficult. 
In Fig. 510, which represents a bolted cylinder, there will be observed 
radial set-screws attached to the flange on the crank-head, whose func- 




FiG. 503. 

tion it is to secure and adjust the alinement of the cylinder and the 
bed-plate. 

The cover of the cyhnder is bolted to the cylinder proper by means of 




Fig. 504. 



a series of studs, whose inner end is tapped into the flange or solid metal 
of the cylinder, and whose outer ends carry nuts by which the cover is 
held steam-tight to its place. The joint between the cylinder and the 



ENGINE CYLINDER, PISTON AND PISTON-ROD 



571 




572 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

cover is a ground or metal and metal joint and requires no packing, 
or at most a gasket of oiled paper. Many designers use a cross-section 
of the studs so that in case of entrapped water the stretch of these bolts 
within their elastic limit shall open the joint enough to release the water. 




These cylinder-covers are often cracked across by water, and precautions 
must be taken to prevent such accidents. The cover is usually so 
modeled on the inside as to enter the bore of the cylinder and help to 
reduce the waste room or clearance. While Fig. 510 shows the head 
covered with a false plate, it is easily seen that the head might be cast 



ENGINE CYLINDER, PISTON AND PISTON-ROD 



573 



with hollow recesses in it in which steam can be circulated to prevent 
heat-losses and form a part of the steam-jacket to reduce condensation 
of the first steam on entering. The objection to the jacketed head is 
its continual supply of heat to the exhaust steam which is leaving 
the cylinder (see paragrafs 228 and 316).' The jacketed head is the 
largest area exposed to the entering steam, and is the most effective 




Fig. 510. 



in reducing initial condensation. Jacketed and other forms of head 
will be noted in Figs. 436, 496. 

The cylinder should be bored in the shop in the position in which it 
is to work. That is, a vertical cylinder should be bored on end, and a 
horizontal cylinder on its side. The reason for this is that the weight of 
the metal in the cylinder will distort it while the boring-tool develops a 
true cylinder. The cylinder which was bored vertically will sag and 
shorten the vertical axis when laid on its side, while the cylinder bored 
horizontally under strain of its own weight will go out of round when 
stood up on end so that the weight is taken off. 

The valve-chest is usually cast on the cylinder and in one piece with 



574 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

it so as to avoid joints. It will be constructed with a convenient lid 
or bonnet so that access can be easily had to valves and seats for exami- 
nation or repairs. The nuts on all studs of covers, lids, and bonnets 
will be carefully case-hardened to prevent injury from wrenches. And 
it is best to use only fixed* or box spanners accurately fitted to such 
nuts in order to avoid mutilating the corners. Such wrenches and 
spanners accompany every well-made engine. 

376. The Counterbore. By reference to Fig. 510 it will be observed 
that the bore of the cylinder at its two ends is slightly larger than the 
standard diameter through the rest of its length. This enlargement of 
the bore is called the counterbore, and its object is threefold. 

1. The piston in its motion should slide up to and beyond the end of 
that part of the cylinder on which the piston bears. In other words, it 
must traverse the entire length of the cylinder-bore proper. Without 
this precaution the pressure of the piston or its rings, wearing the bore 
up to a certain point only, will develop a shoulder at that point, and any 
change in the length of the connection between the piston and crank-pin 
caused by wear will make the piston bring up against this shoulder at 
one end or the other and cause a knock or pound. If the piston laps 
over into the counterbore at each stroke, it wears the whole length 
equally and no shoulders should occur. 

2. The slight enlargement simplifies the operation of getting in 
elastic rings such as are fitted to most pistons to make them steam-tight. 

3. The counterbore, undergoing no wear in use, serves as a truly 
cylindrical surface to re-establish the axis of the cylinder for reboring 
in case of wear. 

The counterbore and the steam-passages into the cylinder should 
be so related to each other and to the bore proper of the cylinder that 
the pressure of steam entering the cylinder should not come upon the 
piston sidewise, but from the end. If this detail is disregarded, the 
steam-pressure will at admission drive the piston against the opposite 
side of the bore and cause a disagreeable knock or pound. This will be 
worse at the head end, because the rod is more flexible. It is mitigated 
by prolonging the piston-rod out through the head. 

377. Cylinder-Cocks and Relief or Snifting-Valves. To drain the 
cjdinder and to get rid of excessive water of condensation, a hole is 
drilled into each counterbore at the lowest point of the cylinder, into 
which a pipe-connection is tapped. These drain-pipes are controlled 
by valves, and discharge either into a closed tank, or into the condenser 
or a drain, or simply into the open air, as may be convenient. The 
valves are called cylinder-cocks, and will be opened when the cyhnder 
is to be warmed at starting, or when it gives indications of excessive 



ENGINE CYLINDER, PISTON AND PISTON-ROD 



575 



water by the noise of snapping or cracking, like a hammer-blow, which 
is the indication of its presence. In large cylinders, which will be weak 
to resist the action of water, and in marine engines, where the pitching 
and tossing of the boilers may cause abnormal quantities of water to 
come over with the steam, automatic rehef-valves are provided to open 
of themselves in such an emergency. These snifting-valves are usually 
plain conical valves opening outwards, and held in place by a coiled or 
flat spring. The tension of such a spring is made greater than the 
usual steam-pressure, so that in normal conditions they remain on their 







Fig. 511. 



seats. Excessive pressure from water hfts them off their seats against 
the spring and relieves the cylinder and its cover. Fig. 511 shows two 
types of relief- valves and a form of breaking cap. A special brass 
fitting screws into the cylinder, and has a thin plate soldered over the 
large opening, but not too strongly. The plate is easily renewed if 
forced out by excess of water. 

378. The Cylinder-Jacket or Lagging. The radiation of heat from 
the cyhnder must be reduced as far as possible. This is desirable, first, 



576 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



to diminish condensation of steam which ought to do work in the 
cyHnder, and, second, to keep the engine-room cool. Furthermore, the 
doing of work in the cyhnder by expansion condenses a certain weight 
of steam, and it becomes desirable to diminish internal waste in the 
cylinder from re-evaporation of such condensed steam as far as possible. 
For this purpose the walls of the cylinder are often cast hollow so that 
live steam from the boiler can circulate through these hollow passages 
and keep the working bore hot. This hot steam surrounds the working 
bore, and the appliance to keep it there is called a steam-jacket. Fig. 615 
shows the steam-jacket and cylinder, and Fig. 510 shows the valve-chest 
thus jacketed. The constructive diffi- 
culty of the hollow bore comes from 
the unequal expansion of the outer 
and the inner wall in cooling. This 
makes the inner wall very liable to 
crack in service in large engines. 
.The difficulty has been met in two 
ways. First, by making the bore of 
the cylinder an inner lining which 
fits in properly prepared shoulders cr 
flanges in the outer casing which forms 
the jacket. The joint between the 
lining and the rest of the casting is 
made by copper rings. The cylinder- 
cover closes down upon this lining to prevent displacement. The 
other plan is not to make the jacket a continuous casting, but to 
have its two halves united by an expansion-ring of some flexible metal 
which will make the joint steam-tight, but will yield to changes of 
length (Fig. 512). 

Outside of the jacket, or protecting the cylinder-casting proper if 
there is no jacket, is a provision for some non-conducting material. 
This may be hair-felt, mineral wool, or wood, or combinations of these 
with asbestos board. This non-conducting material may be held in 
place either by narrow strips of wood, or by thin staves of cast-iron, or 
by a sheathing of Russia sheet iron. This is called a lagging. The 
choice of method will be fixed by the taste of the designer, and it may 
be embellished by the use of polished rings. Its object is to prevent 
radiation and at the same time to produce a pleasing effect to the eye 
(Fig. 604). 

379. The Structure of the Piston. The piston is to fit the bore steam- 
tight. It must therefore have sufficient area of contact with the bore 
to bear efficiently and to accommodate the packing devices. It is 




LEAVITT JOINT. 



CORLISS JOINTi 



Fig. 512. 



ENGINE CYLINDER, PISTON AND PISTON-ROD 577 

therefore not calculated as a rule, but receives a length which is the= 
result of experience in the main. By reason of its size it would have 
unnecessary weight in large engines if made solid, and for the sake of 
Ughtiiess it is usually to be met in one of three forms : 

1. The solid piston, which is usual in small engines only. 

2. The box piston. In this the two faces of the piston are of solid- 
metal, but the spaces between them are made hollow by the use of cores, 
in casting, having the shape of a sector of a cylinder. Such cores form 
the piston into a series of internal chambers separated from each other 
by partitions which form stiffening ribs to prevent the piston from being 
forced out of shape. These cores, which form the chambers, are sup- 
ported upon feet of their own material which will leave holes in one or 
the other face out through which the material of the core is withdrawn. 
These holes in the face are then tapped, a plug is screwed in to refusal, 
and the metal of the plug cut off. The hollow where the core has been 
is at first filled with air only, but water or oil is apt to work through the 
pores of the iron into the cavity more or less. Some ugly accidents have 
happened from the heating of old pistons without a previous venting 
of these cavities. An accumulated pressure from air or gas heated to a 
high tension has rent the piston in pieces. 

3. The spider-and-follower piston. In this the piston is made in 
two pieces or more. The solid part, called the spider, consists of one 
face and the side or contact surface. This cup or dish-shaped part eon- 
tains the center hub to which the rod is attached, and from it to the 
sides radiate ribs which give stiffness and strength. It is these radiating 
ribs from the central body or hub which give it the name of spider. 
The other face of the piston is a separate plate which bolts to the ribs 
or hollow of the spider and forms the cover. It is called the follower. 
When the follower, instead of forming the entire face, is merely a ring 
rather than a plate, it sometimes retains its older name of junk-ring. 
It received this name when the packing material was hemp or junk and 
access was had to the grooves in which this junk was packed by the 
removal of the ring. In most cases the follower-plate comes off the 
piston or spider on the side opposite the piston-rod. An exception is 
met in beam-engines, where the piston-rod goes out through the top of 
a vertical cylinder. Convenience of access from the top induces the 
follower plate or ring to be on the piston-rod side in this case. The 
follower plate or ring is fastened to the spider by bolts which are them- 
selves made of bronze, or their nuts are. The object of this practice 
is to prevent the nuts rusting fast to the thread and refusing to come off. 
The piston in most cases is made of cast iron. This is because of the 
convenience of shaping and fitting, but furthermore because it is desir- 



578 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

able that the piston and cylinder-bore should be of the same metal or of 
equal hardness. Recently some locomotive pistons have been made of 
steel disks and of aluminium or other bronzes, for the sake of lightness; 
but when steel is used a cast-iron outer shell has often been fitted which 
forms the contact-surface with the cylinder and carries the packing 
appliances. It is likely that steel and strong metal-plate pistons will 
come more and more into use. 

r In vertical engines it is common to round the upper face of the piston 
or to make it convex, while the lower cylinder-head is made similarly 




Fig. 513. 



convex upwards and the lower face of the piston correspondingly con- 
cave. The object of thus doming these surfaces is to cause them to 
shed water outward from the center to the bore so that it will pass into 
the exhaust-passages and the drip. 

Figs. 590 and 601 show the typical soUd piston; Figs. 510, 513, and 
many others, typical box or hollow pistons; and Fig. 514 the usual form 
of follower piston used in locomotives. Fig. 515 shows the new type of 
steel-plate piston. 

380. The Piston-Packing. The piston cannot ordinarily be fitted to 
its bore so as to be steam-tight. This is, first, because the piston and 
the bore are fitted cold and will expand unequally when heated. If the 



ENGINE CYLINDER, PISTON AND PISTON-ROD 579 





Fig. 514. 




Fig. 515. 



580 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

bore expands more than the piston, it leaks. If the piston expands more 
than the bore, it is seized by the latter too tightly to be moved if it was a 
close fit when cold. Furthermore, wear of the contact-surfaces would 
make a solid piston fit loosely in the bore after a certain time and permit 
leakage. If the piston leaks, steam passes directly from the inlet to the 
exhaust-pipe, and so to waste without doing work. This increases the 
consumption of steam per horsepower and the consumption of coal. 
For such reasons some form of packing appliance to make a steam-tight 
joint and allow for expansion and wear has been used from the beginning. 

In the first steam-engines made, before the machine tool known as 
the boring-machine had been invented, the cylinder was cast as nearly 
cylindrical as possible and smoothed by hand. A joint between the 
piston and the cylinder was made by coiling a plaited square gasket of 
hemp-fiber or junk into a wide groove formed in the piston. This gas- 
ket was made of an eight-strand braid, and was held in place and forced 
outwards by screwing down the follower-plate or junk-ring (hence the 
name). These elastic or fibrous packings were adequate for low pres- 
sures and low temperatures, such as prevailed in the early days. They 
can still be used for water-packings, and combinations of canvas and 
rubber may still be used under conditions of this sort. What is known 
as the cup leather packing can also be used with cold fluids. An 
annular ring of leather, having an exterior diameter greater than that 
of the bore, is pressed into the bore when wet so as to turn cup-shape, 
and is drawn up against the piston and held in place by a ring acting 
just like a junk-ring. The cup of the leather ring or disk which lies 
against the bore is pressed outwards by the pressure of the fluid, and 
leakage is prevented. 

The only way in which pistons can be made tight without packing- 
devices is by the use of what is called leakage-grooves. These are a 
series of shallow grooves turned in the sides or bearing-areas of the pis- 
ton and so numerous that the pressure leaking from one groove to the 
next shall not have time to establish itself in all of the grooves and pass 
from the last into the exhaust side during a period occupied by one 
stroke. The principle is that pressure must be fully established in the 
.first groove before steam will leak from the first groove through the 
narrow space between the piston and bore into the second groove, and 
so on. Such pistons would not be tight if they stood still or moved at 
low velocity. At high speeds they serve their purpose if there are 
enough grooves, but their presence makes the piston of unusual length 
in the direction of its motion. The grooves become filled also with the 
lubricating material, and with water of condensation, which helps to 
make the joint tight. They have less friction than elastic packing. 



ENGINE CYLINDER, PISTON AND PISTON-ROD 581 

381. Piston-Rings. By far the most usual method of making a piston 
steam-tight is by means of rings which fit in grooves turned in the 
bearing-surface of the piston. It is intended that these rings shall fit 
their grooves on their sides closely enough to prevent leakage around 
therii, and that they shall be forced radially outwards with sufficient 
force to prevent steam leakage between them and the bore. Such 
rings are called piston packing-rings, and they will differ with different 
designs according to their material, according to their number, and 
according to the method used to keep them tight against the bore. 

The materials used for piston-rings are cast iron, steel, and composite 
metals. The advantages of cast iron are, first, its cheapness; second, 
that it has the same hardness as the bore and so does not wear it unduly; 
and third, its convenient elasticity. 

The advantages of steel are its elasticity and that it is not as fragile 
as cast-iron rings. Cast iron has been known to break from shock or 
vibration while in service and cause unpleasant consequences in the 
cylinder. The use of steel rings for pistons is attributed to Ramsbottom 
of England. 

The composite rings are brass or bronze rings, or rings of such metal 
in which recesses are cast and in which recesses some soft bearing metal 
like babbitt is cast to form the contact with the cyHnder-bore. The 
object of these composite rings is to obtain a bearing metal softer than 
the bore, so that the wear shall be concentrated upon the rings, which 
are easy to renew. The objection to the steel rings is that they are likely 
to abrade the cylinder by their superior hardness or density, and to 
rebore the cylinder is more troublesome and expensive than to renew 
a worn-out ring. 

The ring in order to be elastic must be a non-continuous ring, or with 
a break at some point in order that its length may vary. This joint 
between the two ends of the ring must be prevented from allowing a 
leak. This is done either by simply making the joint a scarf-joint, or by 
fitting a tongue-piece which shall sHp in the ring at one end while 
fastened in the other and thus close the joint (Fig. 516). It is very 
usual to have two rings, so that the joints in the two rings may be on 
opposite sides of the piston. Fig. 513 shows the rings in separate grooves, 
while Fig. 510 shows two rings in the same groove. 

To press or force packing-rings radially outward against the bore, 
five methods are usual. 

1. To depend on the elasticity of the ring itself. This is appli- 
cable to pistons up to 16 or 20 inches in diameter, but is not desirable 
for larger sizes. It is used both with steel and cast-iron rings. The 
ring is turned as a solid ring to fit a diameter larger than the bore. 



582 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

Usually the proportion is a quarter of an inch larger for each foot of 
diameter. The finished ring is then sawed apart and sufficient metal 
taken out at the joint to permit the ring to be squeezed together so 
as to enter the cyHnder. It will tend to expand to its original size 
against the restraining bore, and this pressure makes a steam-tight joint. 
Such rings are called snap-rings. They do not guide the piston at all, 
as they are loose in the grooves sufficiently to move freely, but not 
enough to leak. To keep the radial pressure of the ring against the 




^ffii 



^^ ^ ^ ^. 



Fig. 516. 



bore the same at every point so as not to wear the cylinder unequally, 
the thickness of the ring should be graduated and should be different 
at different distances from the joint. 

2. The packing-ring proper of cast iron and steel is forced outwards 
by an inner or spring ring. This is a common plan in large vertical 
engines where the weight of the piston does not come upon the rings 
or springs. It can also be used in horizontal engines of medium size 
(Fig. 510). 

3. Flat springs, pushing the rings radially outwards at several points 
of the circumference. This is a favorite locomotive design and for 
larger horizontal engines (Fig. 514). The flat springs can be adjusted 
by nuts or screws to give greater or less tension, and in horizontal engines 
with heavy pistons the tension on the lower springs may properly be 
made greater than on the upper. This type is applicable only to pistons ■ 
of the follower type, and the adjusting of the springs requires that the 
follower be removable. In vertical engines these springs should all be 
set out equally, and a clever design by which a taper pin exerts radially 
a pressure on the studs which carry the springs is shown in Fig. 517, 
whereby the cover does not have to be removed. 

4. The packing-ring may be forced outwards by positive means, 
such as screws or wedges or combinations of them. The idea is that 
with a true bore there is no occasion for elastic pressure upon the packing- 
ring, but that it causes unnecessary friction. If the ring is set out just 
enough not to leak, and the bearing-contact of the ring and bore is large 
enough, there is no occasion for give or take in the ring. The wedge 
or screw is variously applied, either to enlarge the diameter of a split 
ring by separating its ends or by pressure exerted radially upon the 



ENGINE CYLINDER, PISTON AND PISTON-ROD 



583 



packing-ring or the inner bull or junk-ring. This type of packing is 
applicable, of course, to follower-pistons only. 

5. Steam packing. Fig. 518 shows a plate piston packed with two 
rings. The groove behind each ring is connected at several points 




Fig. 517. 



through small holes with the steam-pressure acting on the piston, so 
that the packing-ring is forced outwards by an elastic pressure of steam 
behind it. It is usual but not necessary to make these packing-rings 
in segments which overlap each other so as to prevent leakage at the 
joints, whereby the steam-pressure does not have to overcome any 



584 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

resistance in the metal of the ring in forcing it out. When steam is shut 
off, the steam-spring ceases its action and lessens the friction in the 
cylinder. This form of packing was first associated in America with the 
name of Dunbar and has been much used. 




Fig. 518. 



A modification of the principle of steam piston-packing has been 
ingeniously applied in some large horizontal engines with a view to 
diminish the friction of the piston and its tendency to wear the bottom 
of the cylinder. Steam is admitted through a hollow piston-rod to a 
place on the bottom of the piston, extending like a groove part way 
around its bottom surface. The area of this groove is calculated so that 
with the usual steam-pressure the upward reaction of the steam in 
it which comes from the hollow rod shall just balance the weight of the 
piston. Rings prevent the steam from leaking out of the groove, and in 
normal conditions the piston should slide upon a layer of steam and 
without metallic contact with the bore, so as to be nearly frictionless. 

38^. The Piston-Rod. The piston-rod has to transmit the motion of 
the piston to the mechanism outside of the cylinder. It has to with- 
stand both push and pull, and the former without bending. It is rarely 
massive enough to have no tendency to bend with the weight of the 
piston when the latter is at the head end of horizontal engines. If 
calculated as a pillar for compression, it will be abundantly strong to 
resist tension provided that it be properly secured in the piston. The 
piston-rod has also to withstand the tendency to abrasion or to wear out 
of round where it passes through the cylinder-head and its stuffing-box. 
For these reasons a great many piston-rods are made of high-carbon 
steel which has been treated by the process known as cold-rolling, which 
gives it a particularly dense, hard, and close texture on the outside, 
and so increases the modulus of elasticity as to increase its resistance to 
bending from the weight of the piston. The usual methods for fastening 
the piston-rod to the piston are five: 

1. The piston-rod is threaded and the piston screwed on it with a 
thin jam-nut or set-screw, to prevent unscrewing (Fig. 515). 



ENGINE CYLINDER, PISTON AND PISTON-ROD 585 

2. The piston-rod is formed with a shoulder, and between the shoulder 
and the end a straight or tapering surface which ends in a screw-thread 
is turned. The piston is bored to fit the straight or tapering end of the 
rod, and when the rod is in place the thread on the rod protrudes enough 
to take a strong nut. The collar and the taper surface take the push 
of the piston, and the nut takes the pull. These methods have the 
advantages of being cheap, and the joints between the piston and 
rod are easily broken (Figs. 510, 518, 615). 

The objection to the second plan is that the projecting nut requires 
that a clearance be made for it (see Figs. 510, 517), and there is always 
a possibility that the screw-joint exposed to push and pull will in time 
work the nut downward along the threads so that the joint becomes 
loose. When this happens it makes a knock or pound which is hard to 
locate. The nut is liable to corrosion in the cylinder and to rust to its 
threads. Where it may be expected or desired that the joint between 
piston and rod is to be frequently broken, the nut may be made of a 
bronze alloy. 

3. The taper is drawn in by a key of metal (Fig. 514). The end of 
the rod is formed into a tapering or conical surface which fits a corre- 
sponding hole in the piston. A rectangular slot is cut at right angles to 
the axis of the rod, and a similar one across the hole in the piston. These 
slots are so related to each other lengthwise that a rectangular key 
driven through the slot when the rod is in place shall bear in the piston 
upon the end nearest the large base of the cone, and in the rod upon the 
end nearest to the small base. The driving in of the key draws in the 
male cone of the rod into the female cone of the piston with a very 
strong pressure until the key refuses to be driven farther. 

This method is an elegant one, but is applicable to follower-pistons 
only. The key is within the hollow part of this piston, it entails no 
clearance, it is very strong, and the joint between piston and rod can be 
easily loosed if necessary. This is done by the use of a special offset 
key driven after the original key has been removed, and which reverses 
the pressure by which the piston was drawn on the rod, by having its 
bearing upon the opposite ends upon the slot in each. The objection to 
it is its cost and the possibility of the joint working loose from a slack- 
ing off of the key. There is not much weight in these objections. The 
taper of the rod may be either 1 in 32 or 1 in 64, according to the amount 
of force with which it is desirable to draw the one cone over the other. 

4. Riveted rods. The end of the rod with collar or taper surface 
fits the piston and projects shghtly through it. The projecting end is 
then upset and turned back upon itself as a rivet is headed. Such 
riveting of the rod may be done hot or cold. If done hot, the rod in 



586 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

shrinking as it cools draws the piston more tightly against the shoulder 
or the taper. The heat may injure or scale the surface of the rod. The 
advantages of this method are that it is cheap and tight and takes no 
room. The joint cannot be broken without destroying the rod. It is 
a favorite joint in small cheap engines, where the value of the rod is 
so slight as not to warrant the cost of an expensive joint. The cold- 
riveting of the rod does not injure the rod by scaling, and can easily be 
made tight against the least motion. The head of the riveted rod is 
often formed in a cup-shaped depression or countersink. 

5. Shrinkage-joints. This is a very elegant joint for pistons of 
medium size. The hole in the piston which is to take the rod is made 
straight and cyUndrical, but is smaller than the diameter of the rod in 
the proportion of .0025 of an inch for each inch of such diameter. This 
makes a hundredth of an inch for a four-inch rod. The piston is then 
heated to low redness, whereby the hole is expanded sufficiently to 
permit the rod to enter it. As it cools it contracts upon the rod, and 
seizes it with a pressure so great and firm that the rod will part some- 
where in its length before the piston will slip off. The advantages of 
this joint are its tightness; it can be broken by heating the piston while 
the rod is kept cool; it involves no clearance. The objections to it are 
its demand for exact working to dimensions if it is to succeed, and the 
strain on the piston and the effect of heat upon it. This method of 
making joints by shrinkage is often used about the crank for its shaft 
and pin with the same advantages. ' 

In follower-pistons the joint with the rod is often designed so that the 
follower-plate shall cover over it and remove any necessity for clearance 
in the cover. 

The front end of the rod is to be secured to the cross-head. This must 
be a joint easily to be taken apart, since the cross-head must be put on 
after the piston and rod are in place in the cylinder. It will therefore 
be found that much the most usual plans are to thread this outer end 
of the rod and screw it into the cross-head with a jam-nut to prevent 
unscrewing; or to taper the end of the rod and the hole in the cross- 
head, and draw them together with a transverse key; or to spUt the 
metal of the cross-head and close the joint by bolts. The screw plan 
will be used on small and medium-sized engines, and the key on medium 
sized and large. Figs. 525 to 531 will serve to illustrate typical methods 
of securing the rod to the cross-head. 

383. The Stuffing-Box. The hole through which the piston-rod must 
pass steam-tight through the head requires to be fitted with special 
devices to prevent leakage. As in the case of the piston, the rod must 
be surrounded by an elastic and adjustable material which shall permit 



ENGINE CYLINDER, PISTON AND PISTON-ROD 587 

the rod to pass in and out with the least friction, and which yet shall 
seize it tightly enough to prevent leakage of steam when the pressure is 
on and prevent the entraining of water with the outward motion of the 
rod on the exhaust-stroke by a sort of a capillary action. The com- 
bination which is used for this purpose is called a stufiing-box. It 
consists of a sort of annular box or cavity, the packing proper which 
goes into that box, and the gland by which the packing is compressed 
and held in place. There must also be a method for tightening and 
holding the gland. 

The typical stuffing-box is exhibited in Figs. 510 and 598A. It is 
quite usual where the rod enters the bottom of the stuffing-box to force 
a bronze annular bushing into the hole in the cylinder-head so as to 
make the rod fit this bushing quite closely. The advantage o^ the 
bushing is that it can be easily forced out and replaced when it becomes 
inconvenient^ worn. It is preferable to have the softer bushing worn 
by the rod rather than to have the more costly rod worn by the harder 
metal of the cylinder-head. The bottam of the stuffing-box cavity 
tapers inwards towards the rod, and the inner end of the gland likewise. 
The effect of this is to produce a component inwards against the rod 
when the gland brings pressure parallel to the rod, and thus to compress 
the contents of the stuffing-box inwards upon the rod. Fig. 510 shows 
the gland drawn inwards by two stud-bolts. This is a most usual plan 
with rods of medium size. For small rods such as valve-stems the 
arrangement shown in the same figure and in Fig. 598A is more usual 
because of the room which is required for bolts of practical size. For 
such small rods the outside of the stuffing-box, instead of being formed 
into a flange, is threaded, and a hollow nut fitting over the gland will 
draw the latter inwards when screwed upon this stuffing-box thread. 
This is the usual method for valve-stems and similar small rods. For 
large rods above four or five inches in diameter two bolts are not enough 
to draw the gland symmetrically inwards and prevent it from cocking 
or binding side wise, which would cause great friction and wear. Care 
must be taken to prevent this in any case, but with very large rods 
requiring four or six bolts in the stuffing-box, as in marine practice, the 
nuts are often made into small pinions or gears which work into one 
large gear so that the turning of one turns all the bolts at once, as in the 
self-centering chuck. This difficulty is avoided when the gland-nut is 
used. 

For the packing material to be used in the stuffing-box the qualities 
to be sought are elasticity and low coefficient of friction, absence of 
abrasive effect upon the rod, and capacity to prevent and absorb leak- 
age. Early packing materials were hemp and cotton fiber plaited into 



588 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



gaskets and laid in loosely. More recently combinations of cotton in the 
form of canvas with rubber have been much used. The rubber gives 
elasticity, the canvas the quality of absorbing and holding the lubricant. 
The lubricant not only diminishes friction but opposes the passage 
of water. Paper-fiber also has been popular, and hemp with graphite. 
Packings of this class are laid in the stuffing-box in a spiral coil, the 
thickness of the packing material being standardized to standard 
dimensions of the space in the stuffing-box which the packing is to 
fill. Packings of one-half, five- 
eighths, or three-quarter inch 
thickness will be usual in engines 
of medium size. 

The objections to these fibrous 
and rubber packings are first 
encountered with high pressures 
of steam, and secondly with 
high heats. Oxidation and 
abrasion of the fiber under 
pressure and heat and a harden- 
ing of the rubber under heat 
make it necessary to renew the 
packings frequently, and they 
have but a relatively short life 
of entire tightness. This trouble 
is particularly present in vertical 
engines with the piston coming 
out of the bottom of the cylinder. 
Unless the packing be excessively 
compressed so as to cause undue 
friction, the rod will draw water 
out with it past the packing by 
a sort of capillary action. Com- 
binations of asbestos-fiber, which 
is not affected by heat, have 
given great satisfaction in 
stuffing-boxes, but exceeding 
care must be used, both in 
manufacture and in use, that 

there be no hard or gritty particles of the mineral. Where care is not 
taken the rod becomes fluted or scored lengthwise from the abrasive 
action of such hard spots. 

To make a more mechanical method of packing which should lasl; 




Fig. 519. 



ENGINE CYLINDER, PISTON AND PISTON-ROD 



589 



longer and resist both heat and pressure, a wide variety of metalUc 
packings has been made. The principle of such packings is to have a 
series of spht rings whose exterior surfaces slope alternately from and 




Fig. 520. 



towards the rod, so that when endwise compression is exerted by the 
gland they close inward upon it. Sometimes a coiled spring is intro- 
duced behind the gland, so that the compression of the split rings may 



590 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

be an elastic force instead of a positive and unyielding compression. 
Furthermore, such rings are often arranged so as not to fill the stuflBing- 
box space sidewise, but to admit a certain give-and-take if the rod and 
the axis of the cylinder should not happen to coincide perfectly. The 
most striking illustration of this will be found in the method of con- 
struction in the Straight Line engine, Fig. 526. Here the packing is 
really a long cylinder which has a motion around a spherical joint in 




Fig. 521. 

the end of the cylinder to permit of adjusting its own alinement. The 
design of Fig. 521 aims to avoid a difficulty with such metallic rings, 
which form shoulders upon each other in the slight motion upon each 
other one to the rod and expansion by heat and high pressure. Each 
section covers the one next it up to the groove, so that the moving 
parts slip entirely past each other, and no ridge of an unworn area can 
be formed. This has been used with highest pressures. 

Certain forms of metallic packing are shown in Figs. 519, 520, and 521. 
If the piston-rod is to project through the back head, a stuffing-box is 
also required there; but it is of less importance if the path traversed by 
that projecting rod is inclosed in a steam-tight cylinder which it fits 
nearly tight. Provision must be made, however, in this case to get rid 
of water which may accumulate there from leakage. 

384. Air-Valves. In engines of the locomotive class where the 
mechanism of the engine may be expected to run on for considerable 
periods after steam is shut off, provision must be made to guard against 
the pumping action of the piston in the cyhnders. The continual 



ENGINE CYLINDER, PISTON AND PISTON-ROD 591 

exhausting of the contents of the cyUnder makes an inward pressure, 
and dirt, cinders, and other foreign matter would thus be drawn in. 
This difficulty is met by having a valve opening inward attached to the 
steam-chest which will be shut upon its seat when pressure is on the 
valve; but will open by atmospheric pressure and let clean air enter 
when the pressure falls below atmosphere. Fig. 603 shows the principle 
of these air- valves upon a locomotive valve-chest. 



CHAPTER XXIIL 

CROSS-HEAD GUIDES AND CONNECTING-ROD. 

385. The Guides and Slides. The cross-head gets its name from 
the fact that it is the head of the piston-rod, and as ordinarily con- 
structed it forms a T or cross-shaped head to such rod. The cross-head 
and the guides which control its motion are counterparts or comple- 
ments of each other, and the form, number, and arrangement of guides 
will be dependent on the preferred arrangement of the cross-head. * 

The British term for the cross-head is the motion-block. 

The condition which the guides must fulfill is that of keeping the end 
of the piston-rod from bending out of the axis of the cylinder when the 
strain on the connecting-rod produces such a tendency (Fig 369) . The 
plane or planes of the guides must therefore be truly parallel to the 
prolonged axis of the cylinder, and it is the convenience of securing such 
parallelism by means of the level which makes it so desirable that the 
engine bed-plate and the cylinder-axis should be truly horizontal upon 
the foundation. In many forms of bed-plates the guides are formed 
and finished in the bed-plate casting and at the same setting of the tool 
at which the cylinder is bored. This insures a common axis for cylinder 
and guides. Where the guides are loose and need to be set up on the 
bed-plate great care must be exercised in their alinement. 

When the fine- wire axis is established (paragraf 372), this is best done 
by means of special fixed gauges or trammels. In the absence of such 
appliances the ordinary surface-gauge, or better the micrometer surface- 
gauge, may be used. When one guide or one pair has been made parallel 
to the axis, the other guide or pair should be made absolutely parallel 
to the first. To have the alinement of the guides defective is to invite 
wearing at the stuffing-box and wearing of the bore of the cylinder out 
of round, and to cause unnecessary friction and often a knock or pound 
in the engine which is hard to locate; or even a breaking of the piston- 
rod. 

The guides may control the cross-head by action in a vertical plane 
or in a horizontal plane. They may be in number, one, two, or four. 
Their surfaces are exposed to abrasive wear, and they should be massive 
enough or so shaped or supported as to resist the tendency to deflect. 
To resist abrasion they are often case-hardened, and to resist deflec- 

592 



CROSS-HEAD GUIDES AND CONNECTING-ROD 



593 



tion they are often made thicker as the distance from the supporting 
ends increases. 

Where but one guide is used it will appear in one of two forms. In 
the first form the cross-head will be arranged to embrace the rectangular 
guide on all four sides with the piston-rod and cross-head pin in the 



f 

^ 



M-'H 



^JJ— Ciji — W- 



.JL 



III ^ 



t±-^ 



"^-i3^^> 



f^-^- 



-53-J4— 



iJi- 




FiG. 525. 



plane of the guide and below it. The cross-head pin must be far enough 
below the guide (Fig. 525) so that the swing of the connecting-rod at its 
widest amplitude shall clear it. This form of cross-head is used quite 
a Httle in locomotive practice, but care must be taken that it should be 
long enough not to cock or bind upon its guide. This is likely to occur 
with short cross-heads of any form if the line of the resultants due to 
the reaction of the connecting-rod on the pin passes at any time outside 
of the center of the pin, or even near the edge of the bearing surface. 
The other form of single guide is sometimes known as the guide for the 
slipper cross-head, and is shown in Fig. 526. The engine in this case 
usually turns in one direction only, and the guide is a flat plane surface 
with suitable edges to prevent sidewise motion of the cross-head. Fig. 
526 shows also a convenient method for adjusting the plane of the guide 



594 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




CROSS-HEAD GUIDES AND CONNECTING-ROD 



595 



in case of wear of the rubbing surfaces. This form is very easy to 
lubricate. 

When two guides are used they may either embrace the cross-head 
if the guides are in the plane in which the connecting-rod oscillates, or 
the cross-head must embrace them if they are in the plane at right 
angles to that in which the connecting-rod oscillates. If there are four 
guides, they will embrace the cross-head in either arrangement. This 
must lead to the discussion of the cross-head. 

386. The Cross-Head. The cross-head for a single guide has been 
already discussed. With two guides it is much more usual to arrange 
them to guide a vertical cross-head, which is one guided in the plane in 




Fig. 527. 



which the connecting-rod oscillates. With this arrangement the guides 
must be far enough apart to clear the connecting-rod in the angle just 
before half-stroke, when it departs furthest from the cylinder-axis. 
This makes the- cross-head of sufficient extent laterally to meet the 
contact-surface. With such vertical cross-heads the guides niay be 
flat and plane (Fig. 527), they may be cyhndrical (Fig. 528), or they 
may be each in two planes inclined to each other (Fig. 529). The great 
advantage of the cylindrical guiding surface (Fig. 528) is that the 
cylinder and guides are so conveniently bored at one mounting with a 
boring-bar having two cutting heads. This secures coincidence of the 
axis of cylinder and guides. The objection to it is that there is nothing 
to prevent a twisting action except the attachment of the connecting- 



596 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

rod to the crank-pin. It is a very usual method in relatively small 
engines. With any of these cylindrical cross-heads the guide-surfaces 
usually are molded and finished in the solid metal of the bed, and the 





Fig. 528. 



adjustment for wear and for symmetry with the cyhnder-axis under 
wear is affected by adjustments in the cross-head itself. The contact- 
surface of the cross-head is usually made by special metal pieces which 





Fig. 529. 



are called gibs. These gibs may be simply cast-iron shoes, cast-iron 
shoes with recesses for Babbitt or other bearing-metal, bronze shoes, or 
shoes of some wood well calculated to resist abrasion, such as lignum 



CROSS-HEAD GUIDES AND CONNECTING-ROD 597 

vitse. The principle of these gibs is that they shall concentrate upon 
themselves the wear and shall be cheaply renewable. They should 
furthermore have a low coefficient of friction. These gibs being 
detached from the solid metal of the cross-head can easily be made to 
be adjustable in the plane at right angles to the cyHnder-axis, by means 
of screws or wedges or bolts. . Fig. 527 shows the adjustment by means 
of lateral wedges, and Fig. 529 the adjustment by longitudinal inclined 
planes. In early Corliss cross-heads the central part was attached to 
the shoes or gibs by bolts of some diameter which were separately 
adjustable and held by jam-nuts when the adjustment was complete. 
A simple type for small engines is often met in which an occasional 
variation can be made by having the adjustment-bolt fixed in position, 
while washers or liners of thin metal or even of paper are taken out of 
the space between the collar and the gib as wear or adjustment may 
require. 

The cross-head using two guides in the plane at right angles to the 
oscillation of the connecting-rod has the cross-head embrace the guide 
on three sides with gib adjustment. This is a usual adjustment in 
beam-engines such as Fig. 389. The gibs are like those shown in 
Fig. 525; but as they will be on the outside of the guides, their adjust- 
ment becomes very simple by the use of screws passing through the 
solid metal of the cross-head and embedding slightly in the gib. This 
can also be used on the vertical cross-head, but is not considered so 
satisfactory and mechanical an arrangement. Nearly all inverted 
vertical engines are guided in the plane of the connecting-rod when 
they have an A frame, or else make use of the slipper one-guide cross- 
head when they have open frames as in Figs. 380 and 381. 

The four-guide cross-head has been a favorite form for locomotive 
practice and in much stationary practice. It makes a comparatively 
light element, and yet the contact-surface is abundant and generous. 
The two guides on each side of the connecting-rod can come as close 
together as convenient instead of having to be at a determinate distance 
apart. Fig. 530 will show the general appearance of a cross-head of 
this type, which has the further advantage that by generous bearing- 
areas the pressure per square inch may be so far reduced that no appre- 
ciable wear is to be expected during the lifetime of the engine, thus 
simplifying the construction of the cross-head, doing away with gibs 
and their appurtenances. The slipper cross-head has this same advan- 
tage. Where gibs are thought desirable they can be easily introduced, 
or wear may be taken up by the introduction or removal of liners of 
thin paper under the blocks which separate the guides at their ends. 
If the contact-pressure be kept below 40 pounds per square inch of area, 



598 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



and a proper lubricant kept continuously supplied, a thin film of oil will 
be always separating the surfaces, and if they never touch they never 
wear. Care must be taken that the design of the cross-head prevents 
the resultant of pressures ever passing outside of the contact-surface. 
If it does, there will be a tendency for the cross-head to cock or press a 
corner down upon the guides, scraping off the oil and setting up abrasive 
wear. It is best to have the pin on which the connecting-rod swings in 
the center of the length of the cross-head for this reason. The gibs, 
furthermore, should have grooves cut diagonally or zigzag fashion in 

their contact-surface to hold the oil and 
distribute it sidewise over every element 
of the guide. It will be apparent that 
the lower guide needs to be lubricated in 
a horizontal engine which throws over, 
and the upper guide or upper gib in an 





Fig. 530. 



Fig. 531. 



engine which throws under (Fig. 369). The resultant of alternate 
push and pull is always in one direction for the engine which turns 
in the same direction. 

Figs. 530 and 531 show the split metal construction for seizing the 
piston-rod; Fig. 531 the shell type of pin. 

387. The Cross-head Pin or Wrist-Pin. The connecting-rod requires 
a pin on which to oscillate while transmitting its motion to the crank. 
It is usual to make this pin fast in the cross-head and have the con- 
necting-rod swing on it. This, however, can be reversed if necessary. 



CROSS-HEAD GUIDES AND CONNECTING-ROD 599 

The cross-head must transmit the effort to the connecting-rod through 
the axis of the piston-rod and the connecting-rod. Hence the wrist-pin 
must either be borne in a hollow in the cross-head or, if the cross-head 
is solifl, the connecting-rod must have a forked end and take hold of the 
pin on each side of the cross-head. There are objections to this latter 
plan^ to be discussed hereafter, so that it is most usual to support the 
pin so as to have it in double shear. In vertical cross-heads the pin is 
apt to be made a tapering fit in its hole so as to be drawn to a tight 
bearing by its nut. A small key also is used in addition to prevent 
turning (Fig. 529). In horizontal cross-heads the pin is usually inserted 
from above into a proper slot. The guides and a steel bolt through the 
guides keep it from displacement. It is usual to make the wrist-pin 
hollow in order that oil may be introduced through the center, and so 
out by a radial hole to the contact-surface (Fig. 531). In the Porter 
wrist-pin the surfaces outside of the sector of steam effort are flattened 
away so as to form an oil-cellar from which the surface of the connecting- 
rod will continually draw oil upon working surfaces. 

388. Parallel Motions. In beam-engines, where the guides for the 
cross-head can only be secured by braces to the frame, which makes 
their alinement troublesome and uncertain, it has been quite usual to 
dispense with guides, and to control the cross-head by means of jointed 
linkages. These linkages are so designed and proportioned that the 
motion of the cross-head is compelled to be in a straight line, either 
exactly or so very nearly that the error is inappreciable. Such linkages 
are called parallel motions. The best known are Watt's, Evans', 
Russell's, and the Peaucellier cell. (See Fig. 402 A.) Their use is 
restricted in modern practice to a very narrow scope, and the 
student is referred to treatises on kinematics for a discussion of their 
properties. 

389. The Connecting-Rod. The connecting-rod in the typical engine 
mechanism must transmit the alternate push and pull of the steam 
effort to the revolving crank-pin. It must furthermore withstand the 
tendency to bend transversely due to the flinging effect caused by its 
own weight or mass as it passes the half-stroke point and has its trans- 
verse motion suddenly changed (paragraf 274). Furthermore, its 
bearings at the two ends are exposed to friction and wear, since the 
entire pressure on the piston must be borne upon the relatively small 
areas of the pins, and the crank-pin rubs its contact-surface in the 
connecting-rod through a space equal to its own circumference in one 
revolution and under the pressure due to the steam. It will be apparent 
that the flinging strain will be greatest with a long rod and at high 
rotative speeds. The rubbing difficulty will be greatest with high 



600 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

pressures and large diameters, and the wear greatest with high rotative 
speeds. 

The cross-section of the connecting-rod to meet these requirements 
is in most cases an elhptical or oval, or even an elongated rectangle with 
rounded top and bottom having the longer axis in the plane of motion. 
Lengthwise the greatest section is either put at the middle or in more 
modern practice it is gradually tapered from the cross-head to the crank 
(Figs. 526, 537). Flinging effect is zero at the cross-head pin and is 
greatest at a point just behind the crank-pin, or more properly at the 
radius of gyration of the rod. In very long connecting-rods, such as 
are used in river-boat practice East and West, the connecting-rod (here 
often called a pitman) is braced by a king-post trussing of wrought-iron 
rods whereby strength to push and pull is fully retained and yet a much 
lighter rod results than would be the case if stiffness were sought by a 
solid deep rod (Fig. 389) . A section of steel rod which has become much 
used in locomotive practice and elsewhere where the conditions for the 
connecting-rods are very severe is the I-shape section, in which the two 
flanges give strength against deflection and all unnecessary metal and 
weight are withdrawn which would bend the rod (Fig. 376, and para- 
graf264). 

The effort of the connecting-rod tends to deflect the end of the piston- 
rod in a vertical plane. The shorter it is the worse this difficulty. 
With a connecting-rod of infinite length there is no tendency to bend 
the cross-head and piston-rod. Ordinarily for practical reasons the 
connecting-rod will be two and a half to three times the length of the 
crank. It will be apparent that a connecting-rod of finite length intro- 
duces an irregularity into the motion of the piston (paragraf 260). 
The piston has moved through more than half-stroke outgoing when 
the crank is at 90 degrees from its dead-center, and on the return from 
the outer dead-center it has not moved through half-stroke at the 
270-degree point. These irregularities affect the accelerating of the 
reciprocating parts, but in ordinary cases are masked by the fly-wheel 
and by the steam-distribution. 

390. The Stub End. In order to provide for the concentrated strain 
on the crank-pins and cross-head pins of engines an especial appliance 
has become nearly universal. The pins are usually of steel, carefully 
hardened in best practice, and it is desirable that they should not wear 
by abrasion, but that if wear must occur it should be concentrated upon 
the surfaces which bear upon these pins, rather than on the pins them- 
selves. Furthermore, the construction of these bearing-surfaces should 
be such that wear may be easily taken up to prevent lost motion or 
pounding, and that when worn they may be easily and cheaply refitted 



CROSS-HEAD GUIDES AND CONNECTING-ROD 



601 



or replaced. These conditions have brought about the combination of 
brasses, strap, gib and key, or cotter and wedge which is known as the 
stub end of the connecting-rod. 

The brasses are two half-cyhnders which embrace the pin and form 
the bearing. They are called brasses when made of bronze (copper-tin 
alloys) as is usual, and even if made of cast iron. They may either be 
true bronze bearings, or they may be made with recesses into which 
Babbitt or other bearing metal is cast to form the actual contact-surface. 
The special purposes served by the brass or bronze bearing are, first, 
that it is easily cast and tooled; second, it is softer than the steel pin, 
and the wear will be concentrated upon it; third, it has a low coefficient 
of friction in case lubrication should become defective; fourth, it has a 
high conductivity for heat, and so draws heat of friction from the pins. 

In marine practice, and elsewhere where it would be inconvenient 
or impossible to stop for any time, spare brasses can be kept on hand 
to replace those which must be allowed to wear themselves out; and the 
replacing of such worn brasses is not a matter of shop repairs, but can 
be made by simply taking down the joint. 

The brasses should touch each other at the point which divides the 
bearing in two halves. As the bearing wears and lost motion begins, 
the brasses should be filed or scraped down until the wear or lost motion 




Fig. 532. 



is taken up. Another plan is to have the joint open a little when the 
two half-bearings are in place and fill the gap with hners of thin sheet 
metal so that the bearing can be made solid. As the bearing-surfaces 
wear, these liners are successively taken out until the joint comes brass 
and brass, when refitting is necessary. Not to fill the opening between 
the brasses is to invite a cramping of the bearing upon the pin with 
friction heating and all attendant difficulties. In some locomotive 
practice in the past the brasses have been capped so as to incase the 
crank-pin completely and keep dust out. 

The end of the connecting-rod proper bears against the outside of one 
brass while the other is drawn against the first half by a U-shaped forg- 
ing called the strap (right-hand end of Fig. 532). The strap is carefully 
adjusted to the brasses and the connecting-rod end, and is held in place 



602 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



and to its work by the combination which is known as the gib and key, 
or cotter. From Fig. 532 it will be seen that the gib and key in this 
form of stub are counterparts and form compensating inclined planes. 
As the key slides along the gib, the 
width at any section is increased. If 
then the gib and key be fitted in slots 
in the connecting-rod body and in the 
strap so that the key rests against the 
outer edge of the slot in the connecting- 
rod, the effect of driving down the key 
will be to draw the strap back, since the 
gib bears upon the strap, but is free 
from the inner end of the connecting- 
rod slot. By drawing back the strap, 
the joint in the brasses closes together 
and the key refuses to drive. A set- 
screw keeps the key from sliding out,- 
and a solid construction results which 
is nevertheless easily removable and 
adjustable. 

It will be apparent that as the brasses 
wear in the form of stub shown, and the 
key is driven down, the effective length 
of the connecting-rod shortens. In time 
also the slots in the strap and rod end 
will come to match, and the key will 
drive no farther. This difficulty will be 
met either by renewing the brasses alto- 
gether or by fitting in between the rod 
end and the inner brass liners or shims 
of sheet metal which will move the 
center of the bearing outwards as much 
as the wear has shifted it inwards. The 
form of stub shown at the right end 
of Fig. 532 is called an " open stub." 
If open stubs are used at both ends of 
a connecting-rod, its effective length is 
shortened at the two ends by driving 
in the keys. 

It is called a closed stub when the gib or key bears against the inner 
brass directly, with the end of the rod as its abutment bearing-surface. 
The left end of Fig. 532 and the upper end of Fig. 533 show this con- 




FiG. 533. 



CROSS-HEAD GUIDES AND CONNECTING-ROD 



603 



struction using a wedge instead of a gib and key. As the wedge is 
adjusted inwards the inner brass moves towards the outer and away 
from the center. The closed stub thus lengthens the rod to take up 
wear. If a closed stub is used at one end and an open stub at the other 
the distance between crank-pin and piston is varied by the difference in 
wear at the two joints; and if there is no difference in this wear, the 
length of the mechanism remains constant. This plan is much the most 
usual and to be preferred. The closed stub may be applied either to a 





Fig. 534. 



rod whose end is forged solid (Fig. 532), or the strap may be strongly 
bolted or keyed and bolted as shown in Fig. 533. The wedges which are 
much used in modern engines for setting up brasses are operated by 
screws and are fully shown in the illustration. To prevent the loosening 
of keys in large engines and at high speeds, where the set-screw would 
not be enough, the end of the key is sometimes drawn down to a rod and 
threaded. A nut on this rod bears upon a Z-shaped bracket bolted to 
the rod and holds the key in place. It is the trouble arising from shnging 
of the key which has caused the wedge with its bolt to receive preference 
in modern usage. Fig. 534 shows a stub of this type, and illustrates also 
the 1 section of the rod. A form of stub first introduced in marine 
practice is shown in Fig. 535. The gib-and-key construction is aban- 
doned, and the half-brasses are held together in a jaw by bolts parallel 
to the length of the rod. These bolts have to withstand the push and 



604 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



pull of the rod, but they make a very stiff and 
strong stub particularly well adapted for crank- 
pins of considerable length. They are also the 
foundation for very deep connecting-rods made 
of hollow tubes for compression, while through- 
bolts resist the tension as they hold down the 
outer halves of the brasses (Fig. 363). 

Another form of stub is known as the round- 
end stub. The end of the connecting-rod has 
a tapering hole within which is inserted a bronze 
bushing which fits the taper on its outside and 
the cyhndrical pin on its inner side. As wear 
takes place, the split in the bushing is filed 
out, and the bushing forced a little farther into 
the taper hole whereby it is closed together. 
This is particularly adapted for parallel rods 
and side rods of locomotives, where it is neces- 
sary that the length between the centers should 
always remain the same. With the gib-and-key 
plan one end of such side rods had to have 
double keys, one outside the brasses and one 
inside. Sometimes this cylindrical bushing plan 
is used without a split and provision for ad- 
justment. When wear has become enough to 
be annoying, the worn bushing is thrown out 
and a new one put in place. In light rods with 
small pins the solid eye is sometimes split, a 
little metal sawed out, and the split held from 
opening by a bolt. As the bearing wears, 
tightening of the bolt closes up the slit and 
takes up lost motion. 

An interesting provision for taking up wear 
with ordinary brasses is shown in Fig. 536A 
in the Appendix. A cavity behind the inner 
brass is filled with steel balls, and into that 
cavity a set-screw projects. The balls displaced 
by the screw press the brasses outward, and 
yet are practically immovable from an outer 
force. They act like the particles of a fluid to 
exert equal pressure upon the brass. This 
device is the invention of Mr. C. W. Hunt, 
but is open to the objection that the pres- 




L. 



10 — — 




Fig 535. 



CROSS-HEAD GUIDES AND CONNECTING-ROD 



605 




Fig. 537. 




sure from the adjusting bolt through the balls to the brass becomes 
excessive in heavy hands, and deforms the contact surfaces. 

Fig. 537 shows strapless types and combinations of design. 

391. Forked-end Connecting-Rod. Double Rods. When it is con- 
venient or necessary to have the cross-head pin supported at its middle 
and to have the motion taken off symmetrically on each side of the axis 
of the piston-rod, the connecting-rod end may be formed into a sort of 
rounded Y with a bearing on each arm. This bearing will be of the usual 
stub construction, with provision for taking up wear (Fig. 380). The 
difficulties and objection to this forked-end construction are those which 



606 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

result when the two bearings wear unequally. The consequence of 
unequal wear is that one side or the other draws the farther end of the 
rod to one side and against the collars of the crank-pin when it is keyed 
up after refitting. The strength of the connection may be enough to 
keep the rod continually out of straight, causing friction, heating, and 
wear. The only proper way to treat such a forked rod after refitting 
is to take off the crank-pin strap and brasses and, with the brasses of the 
fork keyed up close, test the alinement of the naked end of the con- 
necting-rod with the crank-pin at the inner and outer center. If it 
does not fall in line with the pin, liners must be introduced behind the 
brass on the short side, if it is an open stub, until the alinement is perfect. 
Forked-end connecting-rods are usual with the main connecting-rods 
of beam-engines, where they are made necessary by the support of the 
pin by a single beam. The use of a double beam with the pin between 
them makes this construction unnecessary. 

The symmetrical connection of the cross-head of a beam-engine to the 
central beam of such engines would compel a connecting-rod forked at 
both ends. This would be troublesome and difficult, and for this reason 
it will be found that it is usual to use two short connecting-rods for this 
purpose. Each has two stub ends, and the same difficulty attaching to 
unequal wear requires to be guarded against here. Unequal length of 
these rods springs the cross-head, twists the beam, and gives general 
trouble. The same difficulty is to be guarded against in engines of the 
back-acting type for blowing or pumping, such as shown in Figs. 378 
and 379, where the connecting-rods are attached to crank-pins outside 
of the fly-wheel from the wide cross-head. So critical is this difficulty 
from unequal length of two similar connecting-rods that the proper con- 
struction for such a case is to have the cross-head merely pinned to a 
boss on the rod so that it may yield and adjust itself to such slight 
inequalities of length. Many massive cross-heads have been cracked 
from inattention to this detail. 

Small connecting-rods which can be hollow are frequently arranged to 
have a key at one end (or even in the middle) set up the brasses at both 
ends. A rod which passes through the hole in the bore bears against 
the brass at one end and against the key at the other. The term pitman 
sometimes applied to a connecting-rod should be limited to either a 
massive or long connecting-rod or to the connecting-rod which couples 
a vibrating beam or treadle to a revolving crank. The latter is its 
proper use, but it has been sanctioned by usage as a name for those 
wooden rods, stiffened by iron forgings on top and bottom, which are 
used as connecting-rods for the marine engines of the Western rivers. 
The mining origin of the term has been already referred to (paragraf 277). 



CHAPTER XXIY. 

CRANK-SHAFT. ECCENTRIC. FLY-WHEEL. 

395. The Crank-Shaft. The effort of the steam-pressure PA upon 
the piston is transmitted to the crank-shaft through the crank-pin. 
The arrangement of the shaft as a whole must therefore be conditioned 
by the number of cyUnders, and their arrangement respecting each other. 
The construction of the side-crank and center-crank designs also deter- 
mines the arrangement of the cranks and pins upon the shaft. The 
illustrations of types chosen hitherto for illustration present these differ- 




FiG. 540. 



Fig. 541. 

ences. The principal point to signalize is the distinction between single 
and multiple cranks; and the necessity for bearings close to the effort of 
the connecting-rod. The double crank produces less lack of balance 
and makes a stronger crank-pin. Fig. 540 shows the overhanging crank- 
pin construction of a cross-compound engine either horizontal or vertical; 
Fig. 541 gives the triple or three-throw crank-shaft intended to be sup- 
ported on four bearings with each crank double. 

The British name for the crank is the throw. Constructively it is a 

607 



608 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

beam loaded at one end and fixed by the resistance to be overcome at 
the other. The pin is the point of appHcation of the load. 

396. The Crank-Pin. The crank-pin is usually of high-carbon steel. 
It requires to be very solidly inserted into the eye of the crank, and to 
this end three methods are usual. First, it may be forced in by a press. 
The hole in the eye is made cylindrical, and the end of the pin which 
enters the eye receives a very slight taper at the very end, but the 
cylindrical contact is practically of the same size in the eye and the pin. 
The pin is then coated with white lead and forced into the hole, which 
is a little too small for it. This is done either by hydraulic or screw 
presses exerting a force of 20 or 30 tons. The second method is to 
shrink the crank upon the pin by the method described in paragraf 382. 
The third plan is to have the pin and the hole taper, while the inner end 
of the pin is finished into a screw-thread on which fits a nut by which the 
tapers are drawn together. In some forms of disk-crank the pin may 
be held with a key. It is very usual to model the crank-pin with collars 
to prevent sidewise displacement of the brass of the connecting-rod 
upon it. On the other hand, many crank-pins are made without collars, 
and the shape of the brass keeps the connecting-rod from the plane of 
the crank, and a plate which bolts to the end of the pin forms a finish 
which the eye seems to demand, and keeps the connecting-rod from 
appearing to slip off. When collars are used it is common to fillet the 
corners rather than to give them a sharp angle where they join the 
bearing-surface. The pin is not only stronger, but there is less danger 
of a binding of the brasses. ' 

397. The Crank. Whether single or double, cranks may be of cast 
iron or wrought iron or of steel: Since the shaft must be of wrought 
iron or steel, the continuous crank which is made in one piece with it, 
must be of the same metal. The cast-iron crank is therefore limited to 
cases where the shaft is built up. The ordinary form of cast-iron crank 
is shown in Fig. 542. Such crank requires to be secured to its shaft by 
means of steel keys inserted partly in the shaft and partly in the hub 
of the crank. It is usually more convenient to make use of two keys 
than to try to get sufficient shearing area in one. A much more usual' 
form of the cast-iron crank is the disk-crank, such as shown in Fig. 526. 
This arrangement permits of balancing the weight of the crank itself 
on the other side of the center of motion, and furthermore gives a con- 
venient space for additional metal which may serve to counterbalance 
the living force of the reciprocating parts. At high speeds, moreover, 
the disk-crank meets less resistance from the air. Where the disk-crank 
is not used in vertical engines a form of balanced crank, such as shown 
in Fig. 543, will be required to offset the weight or unbalanced effect of 



CRANK-SHAFT. ECCENTRIC. FLY-WHEEL 



609 



the mechanism. Some designers have built up cast-iron counter- 
weights upon a steel crank. Fig. 544A in the Appendix sho^/s an 
arrangement of this sort. 

When there are two cylinders to work upon one crank-shaft and it is to 
be a continuous or double crank, the double crank will be forged solid 
if the length of the stroke is not too great. The excess of metal will be 
cut out by slotting, and then the pin turned by mounting the shaft 
eccentrically in a lathe of sufficient size. Of course it is not easy to forge 




Fig. 542. 



such cranks with short distance between them, nor is it easy to get 
them truly at right angles. Built-up crank-shafts, where the crank-pins 
and lengths of shafting are separate or fastened together by shrinking 
and keying, have been much used in marine practice (Fig. 545). For 
light service at high speeds and short stroke as in motor- vehicle practice, 
the drop-forged multiple crank shaft has had considerable acceptance. 

398. The Locomotive Crank and Shaft. The ordinary American 
locomotive is constructed so as to be what is called outside-connected. 
The cylinders and driving mechanism are outside of the frames, and the 
crank-pins are inserted into proper bosses in the driving-wheels. Inside- 
connected engines, with the cylinders and mechanism between the frames, 
require cranked axles and have no pins on the drivers. The inside- 
connected designs have been most popular in Europe by reason of a 
supposed steadiness and because the effect of torsion between the two 
cylinders is exerted on a less length of axle. The cranked axle is, 
however, more difficult to forge. The inconvenience of having the 



610 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

principal parts of the mechanism clustered together under the hot boiler 
and between the frames, and the possibiHty of equal steadiness for the 
outside-connected design, have given the latter the preference in 




America, but for some compound designs of more than two cyhnders it 
is unavoidable to use one cranked axle. The driving-wheels are pressed 
on the axle by heavy hydraulic pressure, and twisting is prevented by 




Constructed by Messrs. John Elder & Co. 
J 




Conatrudted of Whitworths Fluid Pressed Steel. 

Fig. 545. 



Section tlir jugh A.B. 



keys. The crank-pin is also pressed into its boss. Where the length 
of the engine permits, the connecting-rod or main driving-rod acts upon 
the crank-pin of the main or forward driver. In short engines the con- 
necting-rod will go to the rear driver. In the first case the main pin 
will have two bearing-surfaces on it, that for the main rod being nearer 



CRANK-SHAFT. ECCENTRIC. FLY-WHEEL 611 

the face of the wheel. In the latter case the main-rod bearing will be 
outside of the bearing for the parallel or side rod. Where there are 
three drivers on a side the main bearing will be outside, and the side rod 
connecting the main to the front driver will require a pin-joint near the 
main stub so that no cross-strain shall be brought upon it from 
inequalities of level in the track. Locomotive crank-pins seem to 
undergo a structural change from the combined effect of vibration and 
shock to which they are subjected, so that it is a custom to force them 
out after a certain number of miles have been run and have them 
forged over and replaced, to prevent a sudden breakage on the road 
with its attendant disaster. 

399. The Marine Crank-Shaft. For the ordinary paddle-wheel 
service in deep Eastern waters the crank is a double one, forged, and 
built up with inserted pin. The two halves are essentially aUke, 
and with bearings close to the crank in the main frame and within and 
without the wheel. In a very few cases the two halves of the double 
crank are not in the same plane, but one is slightly behind the other in an 
offset eye. The object of this is to diminish the considerable danger in 
all long-crank engines lest the crank settle down upon the lower center 
by the action of the waves upon the propelling wheels when the engine 
is at rest, which makes it troublesome to start. In Western river-boat 
practice with side wheels the shaft is usually not continuous across the 
hull, but the two engines are separate and are separately handled. This 
gives greater maneuvering power in currents and for landing. Some 
special ferry-boats for railway service have also been constructed in this 
way. For marine engines which drive propellers at the stern it is 
apparent that the entire energy which propels the vessel must find an 
abutment against the lengthwise thrust of the screw in the construction 
of the shaft itself. This is done by means of what is called the thrust- 
bearing. This consists of a large bearing in which a sufficient number 
of grooves or rings is formed which fit corresponding collars upon the 
shaft. The area of these collars and their number are proportioned to 
the energy for which they must provide, and the contact-surfaces in the 
bearing are very carefully fitted with Babbitt or similar bearing metal. 
These bearings are also cored so that circulation of water can be pro- 
vided to keep them cool. These thrust-bearings are usually placed 
close behind the engine, so as to be always under the careful scrutiny of 
those running the engine. As the engine will be located as a rule near 
the center of gravity of the hull, there will have to be a number of joints 
in the propelling shaft both for convenience of manufacture and for 
convenience of handling and repair. These sections will be joined by 
flanges carefully and strongly bolted together. Fig. 546 shows the con- 



612 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

struction of the thrust-shaft and propeller section of a marine engine, 
and Fig. 547 the provision made at the stern to permit the shaft to 
pass outwards through the hull. The joint is made water-tight by 
means of stuffing-boxes, and the actual bearing of the shaft is upon 
lignum vitse or similar bearing material. Such shafts of large diameter 
are apt to be made hollow in best modern practice in order to secure 
strength with Hghtness and to eliminate the defects which in solid 
forging are apt to concentrate themselves at the center both of the ingot 
and of the forging which results from it. 

400. The Main or Crank Bearing. The bearing of the crank-shaft 
close to the crank has to withstand all push and pull due to the steam 





J 



ni 



effort for which it is the fulcrum, and also the weight of the shaft, fly- 
wheel and attachments, and the pull of the belt, if one is used to take 
the power off from the shaft. Furthermore, the shaft turning in this 
bearing must remain very carefully in line both back and forth, and up 
and down. 

To meet these requirements the main bearing must have a generous 
area of contact so that alternate pressure shall be unable to become so 
great as to squeeze out the lubricant from the contact-surfaces, and it 
must be capable of minute adjustment to compensate for wear. Fig. 
548 shows a usual construction of such main bearing, in which, instead of 
two half -boxes as in the stub ends, the bearing-surface is made up of 
four segments. These segmental bearings are called quarter-boxes, 
and in the design shown are separately adjustable by means of wedges 
which come down through the massive cap of the bearing. The quarter- 
boxes are the ones which have to withstand the steam effort in a hori- 
zontal engine, while the lower one has to meet only weight. Fig. 549 
also shows the combination of Hners and wedges to keep the center 



I 



CRANK-SHAFT. ECCENTRIC. FLY-WHEEL 



613 




614 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



distance of the shaft from the cyhnder a constant. It exemplifies a 
method of continuous oihng from a well below the bearing. Rings 
may be used instead of chains. Many 
different modifications of the wedge idea 
are to be met in the various bed-plate 
designs, such as set-screws through the face 
or side of the bearing and the like, but the 
same underlying principle is present in all. 
The main bearing requires special and 
abundant provision for oiling, to which 
reference will be made in proper course. 
The other type of construction is the remov- 
able shell which is replaced as it wears. 

The outer bearing or outboard bearing 
of the engine-shaft has already been dis- 
cussed with the necessity for its adjustment 
for proper alignment. It has to withstand 
only the weight of the shaft and the pull 
of the belt. Both bearings should have 
length enough to prevent the shaft from 
bending under the strains to which it is 
exposed when the diameter of the shaft has 
been intelhgently calculated. One or the 
other bearing should have collars to pre- 
vent undesirable endwise motion. These 
collars, however, must not offer any danger 
from a seizing caused by expansion due to 
heat. Such a bearing is said to be " collar- 
bound," and excessive friction is the result. 

401. The Eccentric. This eccentric, when 
not forming a part of the shaft-governor, 
will usually be placed just outside of the 
main bearing. It will be fastened to the 
shaft either by keying or by set-screws or 
by both. In many cases it is forged solid 
on the shaft. By reason of the diameter 
of the eccentric the stub construction is not 
usual or convenient, but the rod fits the 
disk by means of a bearing-surface which is 
called its strap. This strap is made in two 

halves which meet on a diameter at flanged surfaces by means of 
which the two halves are bolted together. The large area of contact 




CRANK-SHAFT. ECCENTRIC. FLY-WHEEL 



615 



due to the large diameter of the pin makes adjustment necessary only 
at long intervals as slow wear occurs, and this is done either by fiUng 
away the joint of the strap or by removing the Uners of thin sheet 
metal, one by one, which were put in there when the joint was first 
fitted.' To prevent sidewise motion of the eccentric strap, it is 
made either to fit in a groove in the face of the eccentric, or the 
eccentric fits in a groove in the strap. The latter plan has some 
advantages, since the strap thus forms a trough within which the oil 




Fig. 549. 



will gather and be retained at the bottom, whereas in the other 
arrangement the oil has a tendency to run off (Figs. 550 and 551). 

It will be made apparent in the later treatment of valves that their 
operation is inost convenient by the use of a crank. To get the desired 
short throw for a crank in a large diameter shaft by cutting its material 
away would be impossible as it would weaken it both against torsion 
and flexure. Hence the expedient of so enlarging the crank-pin of 
such crank to drive the valve that its diameter exceeds the diameter of 
the shaft enough to let such shaft pass full size through the pin which 
drives the valve. The eccentric disk is the result of this process. (See 
paragraf 420, Fig. 570.) 

403. The Eccentric-Rod and Valve-Stem. The components of the 
crank-motion of the eccentric which are not needed to move the valve 
must be provided for as in the main c'onnecting-rod. Hence there will 
be a joint of some sort between the eccentric-strap and the stuffing-box 



616 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

at which the valve-stem enters the valve-chest. In small and short 
engines the weight of the eccentric-rod will be small, so that it will be 
enough to provide a flexible or pin joint at the end of the valve-stem 
without providing a means to guide the latter except that provided by 
the stuffing-box. In heavier engines the end of the valve-stem may 
either be guided by a sUde, or a rock-shaft must be interposed which will 
carry the valve-rod and from which the valve-stem will be driven. 
Where this rocking-shaft or vibrating lever is introduced it furnishes a 
very convenient means to modify the throw of eccentric and valve, and 




Fig. 550. 



also gives opportunity for hooking and unhooking gear (see paragraf 461 
and Figs. 618, 620, 622). The principal joints of such valve-rod and 
eccentric-rod may either be stub ends, or hardened steel pins may be 
used with hardened steel bushings which they fit accurately. The rub- 
bing work is so small that such well-made work lasts indefinitely. 
The eccentric-rod is usually fastened to the eccentric-strap by screwing 
it into the latter with a jam-nut to prevent its working loose; in larger 
engines it will be a taper fit brought home with a key. In very long 
engines, such as are met with in river-boat practice, the eccentric-rod 
will be an open-work trussed structure of flat rods which ends in the 
single flat or square rod guided by the roller-frame by which it is 



CRANK-SHAFT. ECCENTRIC. FLY-WHEEL 



617 



unhooked. The locomotive-rods are usually flat, and are bolted side- 
wise into recesses made for them in a tail formed upon the inner 
eccentric-strap (Fig. 622). 

The valve-stem is the name appHed to the short rod which enters the 
steam-chest and actuates the valve. It will be either attached to the 
valve by means of a yoke which embraces the latter, or by a screw-joint 
with the necessary jam-nuts. The valve-rod is synonymous with the 
valve-stem except where the Stevens cut-off is used, where the valve-rod 




Fig. 551. 



is the massive rod hfted by the toes, which carries a bracket or offset 
to which the valve-stem proper is attached by means of jam-nuts, 
whereby careful adjustment is made possible. 

403. The Fly- Wheel. In early engines turning with a low number of 
revolutions, the fly-wheel required to be of large diameter, and was for 
this reason nearly always distinct from the wheel from which the power 
was taken off. In more modern engines the convenience of having the 
fly-wheel serve also as an element of the transmissive machinery has 
brought around the use of fly-band-wheels, where belts or ropes are 
used to take off the powder from the engine-shaft. It is so much less the 
practice in recent years to use gearing in transmitting from the engine- 
shaft that the fly-wheel is very rarely a toothed wheel. In electric 



618 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

plants the generator mass always is made to discharge the fly-wheel 
function. 

The function of the fly-wheel is threefold. First, to store up excess 
of energy received from the piston in one part of the stroke, and to give 
it out when the effort shall have grown less by expansion. Second, to 
equalize variation in the leverage with which the varying steam-effort 
acts upon the crank to revolve the shaft. Third, to give out or absorb 
energy when variation in the external load or resistance occurs suddenly. 
The fly-wheel is therefore an accumulator and an equalizer, and the 
reserve which it stores will be greater as its mass is greater and the 
leverage greater with which that mass acts. Since large mass means 
great weight, it is often convenient to increase the virtual radius of the 
wheel (mathematically its radius of gyration) , and thus diminish weight 
which causes friction in the bearings. The objection to the large wheel 
is the space which it occupies vertically, and the complication in foun- 
dation which it causes. With large diameters centrifugal force in the 
rim becomes considerable, and may become equal to or surpass the 
tensile resistance of the material of the rim. For these reasons it will 
be found that smaller diameters prevail in modern engines, and that 
roughly the relation of four times the stroke of the engine is likely to 
approximate the diameter chosen. In early engines thirty-foot fly- 
wheels were often to be met, but now eighteen to twenty feet is a large 
diameter, and in center-crank high-speed engines six feet has become 
a large size. 

The function of the fly-wheel as a regulator is quite distinct from that 
of the governor. The fly-wheel is to compensate for instantaneous 
variations, and give out or absorb energy, and maintain a constant 
speed under variations of the equality between effort and resistance 
which are too small to reach the governor and cause a variation of the 
cylinder-effort. For permanent variations, where the load is increased 
or diminished, the capacity of the fly-wheel is soon exhausted, and the 
engine will either increase or diminish its speed. The governor must 
then adjust its mechanism to bring the engine back to speed, and adjust 
the piston-effort to the new value of the resistance. It is often found 
in electric-railway power plants that wide variations occur in the 
current upon the line without the governor showing any appreciation of 
them. This is to be explained by the action of the fly-wheel and the 
absorption and giving out of energy under such instantaneous variations. 
The weight of the fly-wheel must be very largely determined by the 
character of the external resistance. A weight capable of equalizing 
and steadying the variations of the cylinder-pressure and of crank- 
leverage with a constant resistance would not be enough to serve as the 



CRANK-SHAFT. ECCENTRIC. FLY-WHEEL 619 

necessary reservoir when heavy demands of power are made for short 
intervals. The best illustration of such wide variation of resistance is 
the rolling-mill engine, in which only the friction of the machinery is to 
be overcome when the train is empty, but in which the maximum power 
of the engine is taxed when the piece is between the passes and under- 
going the action of the rolls. Rolhng-mill-engine fly-wheels will have 
a weight of from thirty to fifty tons to meet this requirement, and in 
cable-railway and electric-railway practice, and also with the slow speeds 
of pumping-engines, very massive rotors are used. 

404. The Mechanics of the Fly-WheeL The discussions of Chapters XV and 
XVII are fundamental to a computation of the mass to be given to a fly-wheel. The 
effects of inertia brought out in paragraf 260, and the value of the net turning effort 
given in paragraf 263, and the variation of the impelling force due to working the 
steam expansively (paragraf 298) all enter as factors. 

If from the diagrams of effort upon the crank-pin, in Figs. 365, 373, 375, 377, and 
from Fig. 374 in particular, a curve of efforts to turn the crank-pin be constructed, 
it will resemble Fig. 552, The length of the base-line AE being the semi-circum- 
ference of the crank-pin-travel in one revolution, the height of the ordinates should 
be reduced from those resulting from the indicator diagram on the piston area by 
the ratio of 2 to tt to make the areas of effort in the two diagrams check with each 
other. From the beginning of the stroke at A to the point B the inertia of the 
piston and attached parts is being overcome and the uniform resistance RR^ is 
greater than the effort. From the intersection of the effort curve with the resistance 
curve at B to the point F the effort is in excess, the cut-off having taken place at C. 
From F to the end the drop of steam-effort and the compression have neutrahzed 
the forward effect of the inertia, and the effort is again less than the resistance. 
F will be the point of maximum velocity during the stroke, since the effort has been 
in excess from B until the resistance becomes in excess, and B will be the point of 
minimum velocity with uniform resistance. Hence: let 
R = the radius of gyration of the mass forming the fly-wheel, of arms and rim. 

This may be called the outside diameter of the wheel. 
V = the mean velocity of a point at that distance from the axis; practically that of 

the outer periphery. 
W = the weight of the rim, neglecting the arms: = Mg. 
Vb = minimum velocity of rim ; that at B in Fig. 552. 
Vf= maximum velocity of rim; that at F in Fig. 552. 

Then the energy resident in the revolving mass at B will be 

and at the point F, 

so that the increase from the one state to the other or during the angle or time 
represented by BE, 

EF-EB=^(y'F-y'B)- 



620 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

But the excess of steam-effort over the mean constant resistance must be source of 
such increase in energy; this is represented in the diagram by the area above the line 
RR', shown in double-section lines. Rankine called this L.E, and it is quantitatively 
a work in foot-pounds which can be related to the average work of the stroke which 




is supposed equal to the average resistance. Call £^E = m X work per stroke, or m 
times the area ABCDFE for one stroke, which if multiplied by 2N for the strokes 
per minute, becomes 

A^ X 2A' = I.H.P. X 33,000 X m, 
whence 

AE = ^ (F^^ - V'B) = rH.Px33.000Xm _ ' 
Zg ZiS 

If now the variation in percentage of linear velocity on either side of the mean 
velocity V be denoted by K so that a variation of one per cent on either side makes 
K = 0.02, the mathematical expression for K becomes 

^ Vf - Vb 

— V — • 

It may be defined as the coefficient of fluctuation of speed, so that 

Vf -Vb = KV. 

If the fluctuation be assumed to be cyclic in character, no error will be introduced by 
calling 

Vf -i- Vb = 27, 

whence by multiplication 

Vf - Vb = 2KV\ 

making the equation for AE above appear 

AB = J^ (2KV^) = IH.P.X33 000Xm _ 
Zg Z.\ 

48,500,000 X I.H.P. X m 



from which 



W = 



KN'R' 



by substituting for V^ its equivalent (2~RXy. The value of K will vary with the 
variation permissible in the service performed. In rough service it may be from 
0.06 to 0.10. In factory practice with belt drives and no hghting service, from 0.02 
to 0.04. In electric service involving lights, from 0.01 to 0.02, and ordinary variations : 
where variations are excessive and over wide hmits it will be lowered to 0.0016 to 

0.0025. By assuming sets of values for the ratio — the weights per H.P. can be 




CRANK-SHAFT. ECCENTRIC. FLY-WHEEL 



621 



worked out for values of N and R. The factor m will vary with a wide range of 
condition respecting point of cut-off, speed, accelerating and retarding effort, number 
of cylinders, and relation of connecting-rod to crank (Chapter XV). The following 
tables* would appear to give fair average values from a wide generalization. The 
values for m in multiple cylinder engines cover a wider range of limit values — 
perhaps twice the average — than in single cylinder practice. 

TABLE XIX. 

VALUE OF A £^ OR m AS A FRACTION OF THE WORK PER STROKE. 



Cut-off. 


Single 
Cylinder. 


Two Cylinders, 
Cranks Quartering. 


Three Cylinders, 
Cranks at 120°. 


1 . . 


0.35 
0.33 
0.31 
0.29 
0.28 
0.27 


0.088 
0.082 
0.078 
0.072 
0.070 
0.068 


040 


0.2 


037 


0.4 


034 


0.6 


0.032 


0.8 


0.031 


Full stroke 


0.030 







FOR GAS OR INTERNAL COMBUSTION ENGINES. 



Four-cycle, 1 stroke in 4 3.7 to 4.5 

Four-cycle, missing alternate charge 8.5 to 9 




The work stored by the revolving fly-wheel can be expressed in terms of the work 
done per stroke by the following analysis: since 

A2r=|-(2Ky^), 



WV^ aE 

and the work stored in the wheel is -^ — , this latter can be written = ^r-^r^ 

2g ZK 



aE 



The average work done per stroke is Wa = 
work per stroke to the average work per stroke is 



Hence the ratio of the stored 



A^ 




2K 


m 






aE 


2K ' 


m 





If a value for K be assumed, then the quotient will be a factor giving the number 
of strokes whose work must be stored in the fly-wheel to give a steadiness corre- 
sponding to that assumption. If K be made one percent, or the fluctuation be one- 
half revolution on either side of one hundred, the following table results. If K be n 
times one per cent, the numbers must be divided by n. 



From "Mechanics Applied to Engineering," John Goodman, London, 1904. 



622 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



TABLE XX. 

ENERGY STORED IN A FLY-WHEEL IN TERMS OF WORK PER SINGLE STROKE 
OF A DOUBLE-ACTING STEAM ENGINE WHEN K IS ONE PER CENT. 



Cut-off. 


Single 
Cylinder. 


Two Cylinders, 
Cranks Quartering. 


Three Cylinders, 
Cranks at 120°. 


0.1 


18 
17 
16 
15 
14 
13 


4.4 
4.1 
3.9 
3.6 
3.5 
3.4 


2 


0.2 


1 9 


0.4 


1 8 


0.6 


1 7 


0.8 


1 6 


Full stroke . . 


1 5 







GAS OR INTERNAL COMBUSTION ENGINES. 



Four-cycle, 1 stroke in 4 

Four-cycle, missing alternate charge. 



185 to 225 
425 to 490 



46. to 56 
112. to 122 



When the resistance external to the engine is variable and not a constant, the line 
RR' in Fig. 552 is not a straight line parallel to the base, but a curve with a variable 
height or ordinate. The resistance may also go through cycles which are not con- 
current with the engine cycle. The method, however, is identical with respect to 
finding the excess A E and its ratio m to the average work as in the preceding case of 
uniform resistance. 



405. The Stresses in Fly- Wheels. The fly-wheel in rapid revolution 
has its rim in tension by reason of centrifugal force. If the ring had no 
arms, it would be all equally in tension; but by reason of the arms 
resisting extension as the ring expands under strain, a cross-bending 
occurs between the arms if the wheel is solid, and if made up in segments 
this bending is concentrated close by the joints. In the second place, 
as the rim is the most massive part and tends to revolve uniformly, it 
will happen that when the resistance slows down the engine, the arms 
will De flexed by the effort of the rim to maintain uniform speed, and, 
on the other hand, the effort of the piston when the shaft has lagged 
behind will tend to bend the arms in the opposite direction. Both of 
these strains bring a very serious twisting effort upon the keys by which 
the wheel is secured to the shaft. If the wheel is a fly-band- wheel, the 
effort of the resistance comes directly to bend the arms. In the third 
place, initial strains of construction may be present in the wheel, which 
may superpose their effect upon the action of the other t.wo strains. 
These can be greatly increased if the plane of the rim by bad machine- 



CRANK-SHAFT. ECCENTRIC. FLY-WHEEL 623 

work should be out of the plane perpendicular to the shaft. A sort of 
gyroscopic action must occur from the tendency of the mass to revolve 
in the perpendicular plane. The strains from shrinkage in cast-iron 
wheels form a great objection to the use of solid wheels of large diameter 
of this material. 

406. Solid and Segmental Fly-Wheels. Small cast-iron fly-wheels 
can be made all in one piece; the hub (by means of which the wheel is 
fastened to the shaft), the arms, and the rim being all cast at the same 
time. The arms may be straight or curved. When straight or curved 
they are of elliptical, oval, or fusiform section, with the long axis in the 
direction in which the wheel turns. The elongated section gives 
strength against the distortion of the rim as speed varies, and more- 
over opposes the least resistance to rapid motion through the air. The 
straight arm is carefully tapered from the hub to the rim, and is jointed 
to both surfaces by wide and generous fillets. The objection to the 
straight arm, which the curved arm is designed to avoid, is the 
strain of compression in the arms and of tension in the rim, which 
results when the larger mass in the rim cooling after the other parts 
have become solid contracts in such cooling. The straight arm cannot 
yield, but the curved arm allows a slight bending and relieves the rim 
from strain (Fig. 233). Skilled designers and careful handling in the 
foundry will diminish and almost eliminate these difficulties, so that 
the straight arm with carefully proportioned masses will be found char- 
acteristic of nearly all modern work in small sizes and is more workman- 
like and pleasing to the eye. 

The difficulty connected with the shipment of heavy cast-iron wheels 
in one piece, and the considerable extent of the contraction in cooling 
in large diameters, results in the practice of making the wheels in two 
halves. This is further a convenience in erecting the engine. The 
hub is divided, and each half receives an external flange construction 
so that the hub bolts together over the shaft, and the rim is similarly 
cut and flanged on its inside so that each half can be strongly bolted to 
the other (Figs. 553 and 555). The plane of these joints at hub and rim 
is usually different, so that the bolt-strains may not be entirely axial in 
both sets of bolts at once, and to diminish. the difficulty from the ten- 
dency to fly into two halves by centrifugal force. 

For cast-iron wheels of still larger diameter and heavier weight a seg- 
mental construction is usual both for convenience of shipment, handling, 
erection, and avoidance of shrinkage-strain (Fig. 554). The simple fly- 
wheel which does not have to be used as a band-wheel, and has a rim 
somewhat rectangular in section, will have an arm and a segment of 
the rim cast in one piece. The rim-segment will have a length of one- 



624 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



8 FT. FLY, WHEEL 




Fig. 553. 



FLY WHEEL FOR BOSTON SEWAGE PUMPING ENGINE. 




Fig. 554. 



I 



CRANK-SHAFT. ECCENTRIC. FLY-WHEEL 



625 



half the distance on each side of the arm necessary to reach the adjoining 
arm on each side, so as to have an appearance somewhat hke a T with 
a circular cross-piece. The inner end of these arms is inserted in the 
proper sockets in a massive hub, to which they are secured by keys 
(Fig. 554). The rim-segments are joined together by careful fitting 
upon radial planes, and the rim made continuous by a joint which 
appears in several forms. A piece of wrought iron may be inserted 
into a recess in the interior of the rim, and taper keys or carefully fitted 
bolts driven through the rim keep this wrought iron a prisoner. A 
modification of this is to have tw^o or four such prisoners let into recesses 




Fig. 555. 



on the sides of the rim if there be but two, and into the inner and outer 
faces also if there be four. Even better than this is the use of wrought- 
iron prisoners which are inserted when red-hot into recesses in the rim, 
so that their contraction on cooling shall draw the joint together with a 
force which is measured by their cross-section. These prisoners may 
be of sections of an I, or they may be of the shape of an oval hnk. The 
recess which they fit enables them to be hammered solid while hot, and 
their projection or hold upon bosses in the recess forms the joint. Fig. 553 
shows a two-part fly-wheel with interior prisoner, and Fig. 554 a seg- 
mental wheel. Fig. 555 shows an interesting form of rim-joint and its 



626 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

details, in which prisoners are used of I-section, carefully located in the 
axis of the stress, and drawing the two halves together at a point where 
the section is no less than at all the other points of the circumference. 
Stud-bolts through the arms act also to reinforce and stiffen the junc- 
tion. The ribbed form of rim avoids some process weaknesses, but is 
of course unavailable for belt use. Any cantilever or fulcrum action 
at the joint is impossible when the two parts come together over the 
abutment at the end of the arms. 

407. Fly-Band- Wheels. When the fly-wheel is to serve as a belt- 
wheel or in rope-driving, the rim requires it to be wide rather than deep 
radially. Such wheels moreover will usually be of large diameter, since 
the linear speed of the flexible material used in driving should be high. 
Such band-wheels can be made either by the segmental method shown 
in Fig. 554, or (which is perhaps more usual) the joint between the seg- 
ments will be made at the ends of the arms. The arms will be cast solid 
with the hub and form a spider, and each arm will end in a sort of pad, 
which will form the bearing-surface for the bolts which unite the ring- 
segments to the arms and to each other. Such band-wheels have no 
initial strains from cooling. 

408. Steel Fly- Wheels. The increased realization of the advantages 
of high speed (paragraf 280), and the desire to get increased power from 
an old engine or from a given volume occupied, have resulted in the 
design of wheels of steel to get the increased strength. These are either 
made all of steel plate, or of steel plate in the rims with a spider of 
cast-iron arms. The steel-plate wheel has a web or disk of plate, 
either flat if single, or dished if two plates are used. Where the rim 
is to be built up, steel-plate segments are laid on and riveted up to 
form a ring symmetrical with the web, the successive segments break- 
ing joints around the circumference. The rivets are countersunk, and 
when the rim is thus built up the whole is turned up true. With the 
cast-iron spider construction, the rim is similarly built up, the arms 
having pads at their ends which become built in as the rim is formed. 
Steel is also used in composite wheels. 

409. Composite Band- Wheels. Where great width of face is required, 
more than one set of arms becomes necessary to prevent a side flexure 
from unequal tension at different parts of the drum. The unnecessary 
weight of rim caused by the necessity for width if cast iron is used as 
material for the wheel has resulted in the construction of many wheels 
recently in which cast iron is either abandoned or used only incidentally. 
One design makes use of additional wrought iron or steel spokes to with- 
stand tension; next, the use of wood built up in segments for the rim 
with a cast-iron hub and arms; and last of all, the use of steel plate. 



CRANK-SHAFT. ECCENTRIC. FLY-WHEEL 627 

This latter is either used flat or dished as a central web, and the rim is 
built up of the necessary number of plates, laid edgewise if the wheel 
requires no face, and laid tangentially if a wide face is required. 
Mass and strength have been gotten for the rim by the use of iron 
or steel wire wound around a cast-iron or other rim with sufficient 
tension to withstand centrifugal force and supply the mass desired. 

410. Conclusion and GeneraL — Marine engines require no fly-wheels, 
or rather the water-wheel and propeller serve this purpose. The loco- 
motive requires no fly-wheel, since the driving-wheels and the living 
force of the engine and train serve this purpose. For rough work in 
furnaces, rolling-mills, and elsewhere, with quartering cranks a fly-wheel 
is often dispensed with. 

Most fly-wheels of large engines have notches formed in their face 
to make convenient places in which a bar can be inserted in order to 
pry them over the centers if they should be caught there. Marine 
engines have usually special attachments of screw and worm-wheel 
driven by a small donkey-engine for turning them over in port for pur- 
poses of inspection and repairs. Large engines have sometimes a 
special engine to start them turning slowly from rest. Such engines 
have a small pinion meshing into teeth upon the fly-wheel, often internal 
to its rim. As these engines perform the same function as the bar in the 
notches above, they have been called barring-engines. As soon as 
the main engine receives its power and would turn the barring-engine 
at high speed, the governor on the latter throws the gears out of mesh, 
and stops the small engine. 

Geared fly-wheels revolving faster than the engine-shaft have been 
proposed and used. When driven by belts they offer the advantage 
of compactness, and where the driven machinery turns faster than the 
engine they can apply their regulating effect more directly. They have 
been proposed as means of storing energy in central stations and upon 
railways with very steep gradients. The difficulties are those due to 
their friction even with roller-bearings, and the relatively small amount 
of energy which they will store. With steam-turbines the rotor and 
the generator supply all fly-wheel energy required. 



CHAPTER XXV, 

VALVES AND VALVE-GEARING. 

415. The Valve-Gear and the Governor. The reciprocating engine 
has to have a device to admit the pressure of steam from the boiler 
upon the proper face of the piston and to release this pressure from the 
cyhnder when its work has been done. This device will be some form 
of valve or valves, moving within the steam-tight steam-chest which 
\yill form part of the cylinder. To drive this valve or these valves, 
and to time their action relatively to the piston traverse, will require a 
mechanism, to which the name " valve-gear '^ is given. The valve-gear 
has also a most important function in regulating the weight or volume 
of steam which shall enter the cylinder from the boiler at each stroke, 
BO as to admit only so much as is required to do the work of that stroke, 
without permitting the speed to fall off by admitting too little, or the 
engine to speed up by admitting too much. The automatic control of 
this latter function will rest in the governor, which therefore becomes 
closely related to the valve-gear. The difference of the function of the 
governor from that of the fly-wheel has already been discussed (paragraf 
403) ; the governor will not drive the valve-gear as a rule, but will control 
t,he motion imparted to it from the engine-shaft. 

The subject naturally divides itself into three parts: 
The valve. 
, The gear for driving and timing the motion of the valve. 
The gear for regulating the quantity of steam admitted. 
The governor for controlling the valve-gear. 

416. Engine-Valves. General. Lifting, or Poppet Valves. The opening 
which is alternately opened and closed by a valve is called its '' port." 
The contact-surface which is so machined as to be tight is called the 
" face " on the valve and the " seat " upon the stationary part of the 
casting. 

A valve may open and close its port by Ufting from off its seat, or by 
sliding to one side so as to leave the passage free. The sliding-valve 
requires to be lubricated; the lifting-valve does not. Hence at high 
temperatures, as in gas-engines and with highly superheated steam, the 
lifting- valve offers many advantages. 

The lifting-valve is often called the " poppet "-valve, — either 

628 




VALVES AND VALVE-GEARING 629 

because it appears to " pop up " as it opens, or from a fancied analogy 
to the motion of the figures in a puppet-show. For small areas, it will be 
a simple round disk upon the end of its rod or stem, the face being 
either flat or conical (Fig. 560). In these forms they are often called 
mushroom- valves. A simple calcula- 
tion for lift in terms of port diameter 
shows the valve should lift one- 
quarter the diameter of its port in 
the flat-face type to open full area 

of the port.* Such valves rarely lift as high as this on account of 
noise in closing and of leakage during the time of closure. 

The effective area of the port should be so chosen that the velocity 
through the opening should not reduce the pressure on the lower pressure 
side of it by the process called '' wire-drawing " with attendant loss. 
This will be secured if the velocity is less than 100 linear feet per second f 
(paragraf 236) or 6000 feet per minute. 

For large port areas, the balanced or double-seated poppet-valve will 
be used (Fig. 561) by reason of the lessened power required to lift it 
from its seat and its quieter closure. The cut shows the steam inlet 
and exhaust outlet valves for a vertical river-boat beam-engine. The 
cylinder connects to the space between the two disks as shown at the 
left hand, and the partition at the center of the right-hand cut separ- 
ates the pressure and the vacuum spaces from each other. The steam- 
pressure on the exhaust or vacuum side is therefore from within 
upwards on the upper disk and downwards on the lower; while on 
the boiler-pressure side it is upwards upon the lower and downwards 
upon the upper. It will be apparent, therefore, that valves so con- 
structed can be made either perfectly balanced, underbalanced, or 
overbalanced, according to the area and the direction of the pressure. 
They are most frequently slightly underbalanced in river-boat engines, 
where they are much used, because it is convenient to construct the 
valve-seat of the upper valve large enough so that the lower valve will 
pass through it. This means that the small base of the cone in the 
upper seat shall be just larger than the large base of the disk which 

* Let d = diameter of the port, and I the lift. Then to make the surface of the 
cylinder of height I and diameter d equal the area of diameter d the equality must 
exist: 

t The volume V = 2nv filled per minute when the engine turns n times per 
minute, fiUing the volume v per stroke, when divided by the port area, gives the 
linear velocity; since volume = area X length. 



630 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

closes the opening in the lower seat. Balanced lifting- valves of this 
class open a comparatively large area for the passage of steam, and 
have no friction except that of the stems which pass out of the steam- 
chest through the stuffing-box. 

The objections to them, as applied to engines in which the valve-stems 
are parallel to the piston-rod as in vertical engines, are the excessive 
clearance volume which is entailed, and the difficulty of making them 




Fig. 561. 



so that they will not leak. In horizontal engines, where the poppet- 
valves can lift at right angles to the diameter of the cylinder, the loss 
from clearance need not be so great (Fig. 610). 

Poppet-valves are most usually operated by cams either of the 
revolving type (Fig. 608) as in the gas-engine, or of the rocking or 
oscillating type in river-boat practice (Fig. 389) or in blowing-engines 
(Fig. 361). The slow rotative speed in the latter classes favors the 
cam-gear (paragraf 451). 

Poppet-valves are subject to erosion on their contact-faces from the 
passage of steam or gas over these areas; they suffer from deformation 
from heat and pressure, and from the impact effect of rapid and hard 
closure. 

Furthermore, in the simple or mushroom type they control only one 
port area; or if two disks are fitted for balance, they must both operate 
in one chest or perform one function. If one valve-stem is to carry two 
disks to perform differing functions they will be in separate valve-chests, 
and expansion or contraction of the stem will affect the tightness of the 
fit upon the seats. Hence poppet or lifting valves are usual only in 
valve-gear of multiple valves (paragraf 418), with attendant expense 
for the gear. When lubrication can be effective, the sliding-valve is 
the cheaper to make and maintain. 

417. Engine -Valves. Sliding, Rocking, or Revolving Valves. The 
other type of valve opens its port without lifting off the seat, but by 
shding upon it across the opening and exposing it. The pressure is 



VALVES AND VALVE-GEARING 631 

usually downward upon such sliding-valve, pressing it to its seat, so that 
it has to be moved under such pressure. The contact-faces, however, 
are not exposed to abrasive wear from the steam, but the faces of valve 
and seat wear each other mechanically if not kept apart by a film of 
lubricant. 

Sliding- valves may be plane blocks sliding upon a plane seat; or the 
seat may be a segment of a cylinder, or a cone surface, upon which 
slides a cylinder or a cone which fits the seat steam-tight. Such cylin- 
ders or cones may be complete or partial circumferentially; they may 
expose the port by a rocking or reciprocating motion, or the valve may 
revolve continuously in one direction. The rocking or alternating 
motion is the usual one. The plane surface with a plane block recip- 
rocating on it may be called a surface of a hollow cylinder of infinite 
radius, on which rocks a cylinder also of infinite radius, thus making the 
rocking motion the general case. This is the common plug-cock when 
used in taper or conical-frustum form, rocked back and forth by a lever 
which revolves it part way around its axis. It is a very early form, 
and is still used in its old form in some small engines for the sake of 
cheapness, and in a modified form in some large and elaborate designs. 
(Fig. 499.) The objections to the old plug-cock valve are: 

1. The valve and its casing cannot usually be cylindrical, because 
unequal expansion by heat is apt to cause the casing to seize the plug 
with a firmness which will cause valve-rods and pins to buckle and shear 
before the valve will turn. This occurs because the casing is exposed 
to radiation to the outer air and protects the plug from its action. The 
plug will therefore be hotter than the casing, and if fitted snugly when 
cold they will seize together when hot. 

2. If fitted loosely enough not to seize, cylindrical plug-valves will 
leak. To prevent this they are usually made slightly taper, so that just 
the necessary friction and tightness may be secured by adjusting the 
plug lengthwise in its conical seat or casing. These taper fits are not so 
easy to make perfect except with special machinery. Even then in 
large sizes the large end expands more than the small, and for a given 
angular motion the large end slides over a greater space than the small. 
This tends to produce unequal wear and leakage. The taper plug can 
be refitted to its seat when worn, which cannot be done with a cyHn- 
drical fit. The taper is usually one in sixty-four or thirty-two. 

The vibrating-valve can be made, however, into a very satisfactory 
arrangement by either making the plug proper a shell which is inde- 
pendent of the axis of the cylinder in which it turns — this is the Corliss 
valve — or else by cutting away all of the plug except just the surface 
required to close the opening through the casing which the valve must 



632 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



control. This is a feature of the Wheelock valve and of many deriva- 
tives and modifications of the Corliss (see Figs. 562 and 563). They 
present the advantages which belong to an arrangement which opens a 
wide area by a comparatively small motion of the valve. 



"^Kl^S^ 




Fig. 562. 



It will be obvious that these plug or rocking valves can be used either 
for simple or single functions; or they may be made to discharge several, 







Fig. 563. 



since separate ports may be made in the casing coming from different 
directions, and leading in others. 

The great advantage of the fiat slide-valve and seat is the ease and 



VALVES AND VALVE-GEARING 633 

certainty with which plane surfaces can be made in practice, and that 
when the two surfaces are true and of homogeneous material the sliding 
of the valve upon its seat tends to wear the contact always closer and 
diminish leakage. It is this practical consideration which has had 
much to do with the abundant distribution of the flat sliding- valve. 
Figs. 568 and 616 show cross-sections of such valves. 

418. The Timing of the Valve. One, Two, Three, and Four-Valve 
Systems. The elementary function of the valve and its operating gear 
is to time the opening and closure of the ports as respects the piston 
motion. The pressure must be admitted to the working face of the 
piston from the boiler the moment it is ready to move from its either 
dead-center; the exhaust must be opened at the other end of the cylinder 
at the same moment to let the used steam escape. The exhaust must 
keep open throughout the stroke to let the steam escape freely, but 
must close at such point in the piston traverse as shall entrap and com- 
press the steam desired to produce a cushioning effect (paragraf 262) 
and bring the reciprocating parts to rest and help absorb their inertia 
without inconvenient stress upon the crank-pin. These three functions 
will be comparatively constant, whatever the load. The fourth func- 
tion will be to time the cut-off or arrest of admission so as to vary the 
degree of expansion (paragraf 298) in accordance with best economy 
and the load to be borne for that stroke. This will be essentially a 
function timed variably in the piston traverse. It will be noted there- 
fore in detail from the succeeding paragrafs that the timing function 
of the valve-gear relatively to the piston travel will be to secure at both 
ends : 

1. Constant steam-lead; that is, constant admission at the dead- 
center or before the piston is at its dead-center. 

2. Constant release of exhaust. 

3. Constant compression of the exhaust. 

4. Variable cut-off of admission (or constant in the simplest case). 
In vertical engines, it may be desirable not to have these four func- 
tions the same at both ends of the cylinder, but usually they will be so. 

The simplest case will therefore be that in which the admission is also 
constant. This could be realized by four plug-cocks, one at each corner 
of the cylinder as it were, or two for each end, as in the Corliss or four- 
valve design of Fig. 562. The upper pair at the two ends lead boiler- 
steam in alternately; the lower pair lead exhaust-steam out. They act 
in diagonal pairs; that is, the upper at one end is open when the lower 
is open at the other side of the piston. In Fig. 562 these four valves are 
made double-ported so as to open a large area for a small rocking motion, 
and are in the heads of the cylinder. In Fig. 563 the admission-valves 



634 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

are double-ported and the exhaust are single; the valves are in the 
cylinder-casting itself, and not in the heads. This construction, what- 
ever the driving-gear, lends itself easily to all four functions, and par- 
ticularly to constancy of the first three and variability of the fourth if 
desired. The gear must be different in the last case. 

The constancy of the first three, and particularly of Nos. 2 and 3, can 
be secured by keeping the single-function cock for the steam-inlet, or 
by using lifting-poppets for admission, while using a three-way valve 
for the exhaust. Such valve is illustrated in Figs. 564, 565, only for 
this use the outlet marked to boiler should be marked to Head End of 
Cylinder, and that to exhaust marked to Crank End of Cylinder, while 
the outlet to cylinder should be changed to Exhaust Pipe. Such 



FROM BOILER 



FROM BOILER 




FROM CYLINDER 



Fig. 564. 



FROM CYLINDER 



Fig. 565. 



engines are called Three- valve Engines. The steam- valve closure can 
be varied, while the exhaust functions are untouched. The third class 
of two-valve engines would be those in which there was a valve for each 
end of a double-acting engine, having the construction and operation of 
the three-way cock as it is presented in Fig. 564 for the inlet or admission 
functions Nos. 1 and 4, and for the exhaust functions Nos. 2 and 3 in 
Fig. 565. One of these only is required for a single-acting engine. But 
the important consequence must be noted, that the function of Nos. 1 
and 4 has been so tied to Nos. 2 and 3 that to vary No. 1 or No. 4 is also 
to vary Nos. 3 and 4. 

If now instead of the three-way cock, the four-way design is used as in 
Figs. 566 and 567, it will appear that one valve only will do all that is 
required. Fig. 566 shows steam entering to the head end while exhaust 



VALVES AND VALVE-GEARING 



635 



is leaving from the crank end. But the same inflexibihty attaches as 
to the previous case, since the same valve does both the admission and 
exhaust opening and closure. The simpHcity and cheapness of the 
single-valve construction have given it its wide adoption as a system, 
in spite of its theoretical drawbacks. Two-valve types will appear in 
later paragraphs as solutions to secure the greater economy of variable 
cut-off with varying loads. The wide distribution of the single-valve 
engine has made it the simplest and typical form to begin with. In the 
form of the development of the cyhnder or cone into a surface or valve- 
seat which is plane, with a flat block sliding on it, the boiler inlet is 



FROM BOILER 



FROM BOILER 





the steam-pipe into the valve-chest. Opposite to it and below the 
valve is the outlet ending in the exhaust-pipe. The two ports leading 
to the two ends of the cylinder are symmetrically disposed on each side 
of the central exhaust-port, as in Figs. 568, 569. What dimensions 
shall be given to these parts? 

419. Plain Slide- Valve, Taking Steam Full Stroke. The simple case 
forms the starting-point, where all functions are constant, and are 
made to last throughout the full stroke. That is, the engine is to use its 
steam non-expansively (paragraf 296). There will be no interval 
when the cylinder is not receiving steam except at the dead-points. 

As the valve stands in Fig. 569, its length from out to out horizon- 
tally is just the length from out to out of the steam-ports. Both ports 
are closed, but the motion of the valve in either direction will cause 
steam from the boiler to pass into one or the other of the ports to reach 



636 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

the end of the cyhnder and drive the piston. It would appear then 
that the position of the valve shown in Fig. 569 is that which belongs to 
the two dead-centers of the piston. 

It will be further seen that the hollow in the under side of the valve 
has a net length the same as the length between the inner edges of the 
steam-ports. Hence when the valve moves in either direction so as to 
admit steam by its outer edge to either steam-port, by that same motion 
the port at the other end is opened by the inner edge to allow steam to 
escape from the other end of the cyhnder into the hollow of the valve 
which is always in connection with the exhaust-port and pipe. The 
distance between the edges of the steam-ports out to out is immaterial 
within limits, since the only effect of separating these outer edges is to 
lengthen the valve. To do so, however, is to increase the area upon 
which pressure of steam acts to press the valve to its seat, and hence to 
increase the force necessary to shde the valve. The width of the ports 




Fig. 568. 



Fig. 569. 



is fixed by the area which they must have in order to pass the steam 
which the engine requires per stroke without imposing an excessive 
linear velocity for that steam. The length of the port in the direction 
perpendicular to the plane of the paper is conditioned by the diameter 
of the cyhnder, which of course it cannot exceed. It can at best be equal 
to that diameter, but it is more usual to make it somewhat less. With the 
length thus fixed the area of the port should be such that the Knear 
velocity of the steam through the port should not exceed 100-150 feet 
per second, or 6000-8000 feet per minute. 

It is of advantage not to make the port too wide in the direction of 
the motion of the valve to the right or left, since it will be apparent that 
the motion of the valve from this central position to the right or left 
should be equal to the width of the port in order to open it wide. In 
other words, the throw of the valve and the port width should be the 
same under the conditions now being considered. If the valve-throw 
from its central position is greater than the port width, an unnecessary 
force is expended to slide the valve. If the port width is not uncovered 



VALVES AND VALVE-GEARING 637 

by the throw of the valve, an unnecessary surface is exposed below the 
valve to the steam on its way from the valve to the piston, causing losses 
by radiation, by contact, by condensation, and by unnecessary clearance- 
volume, which the steam fills to no purpose. The throw of the valve 
is the distance which it moves from its central position in each direction. 
The travel is the distance which it moves from its extreme position at 
either side to the other extreme position, and is therefore twice the throw. 
If the valve is operated by a crank or a modification of it, the radius 
of the crank will be equal to the throw, and also equal to the port- 
opening. It is susceptible to demonstration that the volume of the 
cylinder and the area of the port-opening increase according to the same 
law when the motion of each is controlled by a crank;* but the exceeding 
convenience of the crank induced its adoption before this theoretical 
peculiarity had been elaborated, and the discussions of paragraf 258 
have shown that it is a very effective device for transforming rotary 
and reciprocating motion. 

430. The Eccentric is a Cranlc. The throw of most engine- valves will 
be comparatively small as compared with the stroke of the piston; and 
in engines of considerable size, when the shaft is of a large diameter, it 
becomes inconvenient and impossible to cut away the large shaft so as to 
get the small crank in the middle of it. It is furthermore inconvenient 
to drive the valve in most engines from a crank at the end of the shaft. 
It does not affect the peculiarity of a crank to enlarge its pin. So that 
if the typical crank AB shown in heavy lines in Fig. 570 have its crank- 

* By reference to Fig. 580 it will be apparent that if the angular velocity of the 
crank-pin be w, the space described by it will be Ria, and the velocity of a horizontal 
piston will be Roj cos «. If the area of the piston be A, the volume to be filled in a 
time dt will be 

A R(a cos oj dt. . . , , (1) 

If X denote the linear velocity of flow of steam through the port in the valve-seat 
whose length is I, and r be the radius of the valve-crank, then during the same time 
dt the motion from its central position for the same angular velocity w will be r cos 
ia dt, opening an area Ir cos w dt through which a volume of steam passes equal to 

xlr cos 0} dt (2) 

Since these should be equal to each other, by equating (1) and (2) the value of x 
becomes 

^ = ^ (")■ (3) 

which is a quantity involving the crank-pin or rotative speed only, which is common 
to both cranks, and the arbitrary constants which fix the linear velocity of the steam. 
In other words, the steam enters at all angles with the velocity determined by cylinder- 
volume and port-area, and not by variation in relation of the crank-angles. 



638 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



pin successively enlarged until the diameter of the latter becomes so 

great that the circle representing it surrounds the shaft which is the 

center of motion of the crank, there will be no difference produced in 

the motion of such a pin as it revolves around the original center of 

motion. The enlargement of the pin has produced an eccentric, in which 

the distance between the center of motion and the center of figure is 

the radius of the original crank. The valve driven by an eccentric is 

therefore driven by a crank (see paragraf 401), and the mechanism 

has the further advantage that the 

direction of the center-line of the 

crank cptn s^ery easily be changed 

with respect to the engine-crank, 

should it be desirable to alter and 

adjust the angular relation between 

these two. When valves are not 

driven by a crank or eccentric, it 

will be found that the motion will 

be given either by cams or by such 

a combination of rods or links as 

to constitute a link-motion. These 

methods of driving valves will be 

discussed in proper course. Fig. 

233 shows the valve driven by a 

crank from the end of the shaft, but in the majority of engines where 

the valve is driven directly it will be found that the eccentric is used. 

421. Setting of a Plane Slide- Valve working Non-expansively. From 
an inspection of Fig. 568 it will be observed that the valve has the shape 
somewhat like a letter D, resting with its straight side upon the seat. 
For this reason this valve has been called the D slide-valve (the German 
name is Muschelschieber, or shell-slider). It will be observed that if 
the piston is at its dead-center at the right of the page in Fig. 569, the 
valve should move towards the left to admit steam to drive it. If the 
piston is at the left of the page, the valve should move towards the right. 
It has been further shown that when the engine-crank is at one of its 
dead-centers, and in a horizontal line in a horizontal engine, the valve 
is in its central position with its crank therefore standing vertically 
up and down. The fair conclusion then is that in an engine working 
non-expansively the valve-crank is 90 degrees distant from the engine- 
crank. Is it to be 90° ahead or behind? 

When the engine throws over (paragraf 289) and the piston is 
on its dead center at the right of the page, it is obvious that the valve 
has been at its right-hand end and has returned to its central position 




Fig. 570. 



VALVES AND VALVE-GEARING 639 

from the right to reach the position shown in Fig. 569. This follows 
because it has been admitting steam for the stroke of the piston from 
left to right, and has closed the port at the left at the end of the stroke by 
coming from the right. It is therefore to admit steam to the right-hand 
port by moving towards the left, which it can only do when the crank 
driving the valve is standing vertically upwards. It is assumed that 
the engine-shaft is at the left as the observer faces Fig. 569, and that the 
rotation is contrary to the hands of a clock. It is further assumed that 
the length of the rod connecting the valve-crank or eccentric to the valve 
is of exactly the right length, and that the valve is connected to the 
eccentric without the interposition of a vibrating arm or rock-shaft, 
which would reverse the motion imparted by the valve-crank. Under 
these assumptions the valve or crank is to stand with its center-line 
making an angle of 90 degrees with the engine-crank ahead of the 
engine-crank in the direction in which the engine is to turn. Hence 
the directions for setting the valve for a non-expansive engine of this 
sort are: 

1. See that the valve-rods are of the right length so that the valve 
opens the ports equally at both ends of its throw. This is called making 
the valve run ^^ square." 

2. Set the main crank of the engine on either dead-center. This can 
be done either by eye, or more exactly by the following process. Turn 
the engine over until the crank is nearly at its dead-center and scratch 
a mark on cross-head and guide which shall indicate such position. Take 
a beam-compass or trammel, such as shown in Fig. 571, and put one 
point in a center-punch mark made on the rim of the fly-wheel while the 
other end rests on a similar prick-punch mark on the frame or bed-plate 
of the engine. Then turn the engine-crank past its center until the 
mark scratched on cross-head and guides comes to coincidence again, 
and the trammel in the fixed point on the bed-plate locates by its other 
end a second point in the fly-wheel rim. It is apparent that the first 
and second of these points in the rim indicate two angular positions 

; equally distant from the dead-center 

u ^^ on opposite sides of it. The point 

If ij half-way between them on the rim 

Y^Q^ 571^ should be the point in which the 

same trammel standing with one 

end in the fixed point on the bed-plate should reach when the engine 

is on its true dead-center. 

3. Slip the eccentric around the shaft in the direction in which the 
engine is to turn until it is 90 degrees ahead of the engine-crank, if this 
can be observed. If not, it is reached when the valve is in its central 



640 MECHANICAL ENGIxVEERING OF STEAM POWER PLANTS 

position, line and line with the edges of the steam-port. Then the 
eccentric is made fast. 

4. Turn the engine through 180 degrees to bring the main crank at 
its other dead-center to test the accuracy of the adjustment. 

If the engine has a rock-shaft which reverses the motion from the 
eccentric, the eccentric should be set 90 degrees behind the engine, or 
at a position 180 degrees distant from that which it occupies when the 
motion is direct. 

If the engine throws under instead of over, the eccentric is still 90 
degrees ahead of the crank, in the direction in which the engine is to 
turn, but is 180 degrees distant from the position which it occupies 
when the engine throws over. 

The expansion of the valve-rod by heat must not be overlooked in its 
effect upon the length of such rods. It will lengthen the rods of a valve 
directly connected, and either lengthen, shorten, or be without effect 
upon the rods which are connected to a rock-shaft. If the rod from the 
eccentric to the rock-shaft and from the rock-shaft to the valve were of 
the same length and of the same temperature, the effect of expansion 
would be compensated. 

423. The B Valve. In some forms of engines, particularly pumps, 

it is desirable that the motion of the valve to admit steam should be in 

the same direction as that which the piston had before it completed its 

stroke. In the D valve these motions are opposite. The valve to meet 

this condition must differ shghtly from the D *valve in its shape, and 

from the form which it takes it is calle • the B valve (Fig. 572). It 

admits steam into the one hollow of the B by sliding past the end of the 

seat or over the edge of an outer 

port. The other hollow is by this 

motion put into communication 

with the other steam-port and the 

exhaust, so that its functions are 

the same as those of two D valves, 

with the exception that the outer _ 

Fig. o72 
edge of the valve does not act. The 

details for setting the directly connected B valve are the same as for 

setting the D valve with rock-shaft. 

423. Engine to Use its Steam Expansively at Constant Cut-ofif. Lap 

in the Slide-Valve. The first modification of the previous simple case 

is where the admission of steam is not to be during full stroke, but the 

steam is to expand at the end of each piston traverse. This must be 

secured by making therefore a period of piston motion during which 

no steam enters. 




VALVES AND VALVE-GEARING 



641 




Fig. 573. 



The valve of Fig. 570 cannot be made to do this by reason of its 
length being only that from out to out of the ports. The valve must 
be lengthened in order that it may close one port and be still sliding 

upon its seat while the piston is 
moving towards the end of its stroke, 
and so that it shall just reach the 
position of opening the new port at 
the other end as the piston comes 
to rest at the dead-center. This 
addition of length must be sym- 
metrical on both sides of the center- 
line, and the increase at each end 
over the fundamental length of the non-expansive valve is called its 
lap, ab in Fig. 573. 

Outside or steam lap may be defined as the amount which the valve 
standing in its central position projects over or laps beyond the outer 
or steam edge of the port at each end. 

424. Eflfects of the Lap. The effects of the lap are: 

1. To accomplish its purpose and compel the steam in the cylinder 
to work expansively, or to produce the cut-off of admission before the 
end of the stroke. It will be 

apparent from Fig. 574, which shows 
a valve on its seat moving from right 
to left and distant from its central ^J 
position a distance equal to the lap ^^ 
on the left-hand end, that it has 
just cut off admission from the left- 
hand end of the cylinder, and must move to the left through a distance 
equal to twice the lap before it can open the right-hand port. It must 
open this latter port at the instant that the piston is ready to begin 
its stroke from right to left. Consequently the piston will have moved 
without admission during a period of angular motion at the end of 
its stroke corresponding to that required to move the valve through 
twice the lap. This is an angular motion corresponding to twice the 
angle whose sine is the lap. This being so, the instructions for setting 
the slide-valve without lap or without expansive working (paragraf 421) 
require to be modified. The valve-crank or eccentric is ahead of the 
main engine-crank not only the 90 degrees there deduced, but is to 
be ahead 90 degrees plus an angle whose sine is the lap. 

2. Hence the second effect of the lap is to set the valve-crank forward 
and prevent the valve being in its central position when the engine is at 
its dead-center. 




Fig. 574. 



642 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

3. The consequence of this second pecuUarity is that the opening of 
the exhaust-hollow in the valve to the two ends of the cyhnder becomes 
displaced, and does not take place as heretofore when the engine passes 
its centers. The exhaust on the expanding or completed stroke is 
preopened, because the valve passes its central position before the piston 
reaches the end of its stroke. It must do this because it has to slide 
through a space equal to the lap in order to open the valve at dead- 
center for the ensuing stroke. This has also preclosed the exhaust-port 
at the right-hand end by the same action and for the same reason. The 
preclosure of the exhaust is of no great disadvantage within limits, 
inasmuch as by this action the entrapped exhaust undergoes compres- 
sion after its outlet is closed and there is produced the cushion which 
was referred to as desirable in paragraf 262. The preopening on the 
expanding side, however, is absolute loss, since tension of the driving 
steam which should have followed the piston clear to the end is released 
into the exhaust, and is wasted. 

425. Inside Lap. When the term lap is used without qualification it 
means lap added to the outside or steam edges of the valve. In order 
to prevent pre-release of the expanding steam, from too early opening of 
the hollow of the valve to the steam-port, the valve-face can be widened 
towards the inside by adding metal which shall narrow the opening into 
the hollow. The normal valve has its hollow of the same length as the 
distance between the inner edges of the steam-ports. When the valve 
stands in its central position, the distance by which the length of the 
hollow is less than the distance between the inner edges of the ports 
amounts to twice the inside lap. Or, in other words, the inside lap is 
the distance which the valve must move from its central position in 
either direction in order to open the corresponding end of the cyhnder 
to the exhaust-port (see cd, Fig. 573). 

426. Effect of Inside Lap. The effects of inside lap are: 

1. To prevent pre-release of expanding steam before the stroke is 
completed. 

2. To close the exhaust-outlet from the cylinder before the 
exhaust-stroke is completed. This produces a compression. The 
effect of this compression on the practical working of the engine is 
fourfold. 

(1) It serves to produce a spring or cushion of elastic steam which 
serves to absorb living force in the reciprocating parts and bring the 
latter to rest by a gradual force exerted to take up lost motion in the 
joints in the direction in which the next working stroke is to strain them. 
Without this cushion the living force of the reciprocating parts must be 
absorbed by the crank-pin, which will produce tension on the joints 



VALVES AND VALVE-GEARING 643 

just previous to the compression-stroke, and compression of the joints 
just previous to the tension-stroke. The steam-cushion makes the 
engine run more quietly (paragraf 262). 

(2) This compressed steam after exhaust-closure fills the clearance 
and port passage with steam otherwise wasted, so that the entering 
steam when the valve opens does not have to fill such waste room. 
Generally the compression should be so calculated that the final pressure 
of the steam compressed into the clearance-volume nearly equals the 
pressure of the steam coming from the boiler. 

(3) The compression caused by inside lap exerts an upward 
pressure upon the valve which tends to counteract the downward 
pressure from the boiler, and thus makes the valve move more easily 
upon its seat for that part of the stroke during which the compression, 
occurs. 

(4) The effect of the compression of the exhaust-steam is to raise its 
temperature and with it the temperature of the cylinder-walls. This 
heat is due to the absorption by the steam of the work done in com- 
pressing it, and consequently the entering steam on the new stroke 
undergoes less condensation in heating the metal. 

Excessive compression due to excessive inside lap or too early closure 
of the exhaust-port diminishes the power of the engine to the extent 
represented by the unnecessary work done in compression. This may 
be enough to lift the valve off its seat, which will be shown by a knock 
or slam when the valve opens and it comes down into contact with its 
seat. 

427. Exhaust-Clearance, or Negative Exhaust-Lap. It will be apparent 
that the inside or exhaust lap will make the exhaust sluggish by reason 
of its tendency to contract the exhaust-passage and produce the effect 
called wire-drawing. This danger is most to be dreaded in engines of 
high rotative speed (paragraf 280); and to avoid this difficulty in 
engines of this class, designers have sometimes lengthened the hollow in 
the valve, so that when it stands in its central position the distance 
between the edges of the hollow is greater than the distance between 
the inner edges of the steam-ports. The distance which the hollow 
lacks to enable it to meet the inner edge of the port is called exhaust 
clearance or inside clearance or negative exhaust-lap. Its use is 
restricted to high-speed engines and to those in which the expansion by 
means of lap is not carried very far. The difficulty would be from 
the too early release of the expanding steam. Negative exhaust-lap 
is sometimes called also exhaust-lead. Its effects are to free the 
exhaust and to diminish back-pressure at the beginning of the return- 
stroke. 



644 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

428. Lead in the Slide-Valve. In slow-moving engines the port may 
open to admit fresh steam just as the piston begins to move. In faster- 
moving engineS; on account of the time taken by the steam to fill the 
passages and clearance, it is usually better to open the valve a small 
angle of the crank in advance of the dead-center. This in effect makes 
the valve lead the piston, so as to bring full boiler-pressure on the piston 
at the very beginning. The definition of steam-lead, or simply lead, is 
the amount which the steam-port is open when the piston is at its dead- 
center ready to begin its stroke. Referring to Figs. 568 and 575, the 
port-opening between the edge of the valve and the edge of the port is 




A'-- L— -Z3.B 



Fig. 575. 



the lead. It will be seen at once that the lead is a matter of adjustment 
merely, while the lap is a matter of construction of the valve. Lead may 
be varied, but the slide-valve lap cannot. 

It will be apparent that the effect of lead on the setting of the valve- 
crank or eccentric will be to increase still further the angular advance 
of the valve-crank beyond the 90-degree advance discussed in paragrafs 
421, 424. The setting of a valve having both lap and lead requires that, 
after the valve has been set in its cerftral position with the valve-crank 
90 degrees ahead of the main crank, the eccentric is to be set forward 
in the direction in which the engine is to move through an angle whose 
sine is the lap plus the desired lead. 

439. Effects of Lead. The effects of sliding the eccentric forward in 
order to give lead at the steam-edges are five : 

1. To increase the angular advance and modify the setting adjustment. 

2. To increase the expansive working by causing the steam-edge of 
the valve to close the admission-port by so much earlier as the valve 
has to move before the piston reaches its dead-center in order to give the 
determined lead. 

3. The effect which these two phenomena have is to increase the 
distortion of the exhaust period. The pre-release and compression are 
increased, or the effect of the inside lap is neutralized at one end and 
increased at the other. 

4. The clearance-volume and port-passages are filled with steam 



VALVES AND VALVE-GEARING 



645 



entering the cylinder before the piston reaches its dead-center, so that 
full boiler-pressure comes on the piston at the very beginning. 

5. The living force of the reciprocating parts is arrested by this 
cushion of hve steam from the boiler. The effect is the same as if it 
were done by the exhaust-cushion, but it is produced by steam which 
must be paid for instead of by steam which would otherwise be wasted. 
430. Setting of Slide-Valve without Aocess to Valve-Chest. Setting by 
Sound. The slide-valve of an engine works in a valve-chest. This is a 
box either cast in one piece with the cyhnder and arranged with lids or 
bonnets by which access can be had to the valve and seat, or else the 
valve-chest is cast separately and secured to the cylinder-casting by 
carefully made steam-tight joints, which are kept tight by bolts. The 

opening of the valve or steam-chest 
for the purpose of setting the valve 
is to be prevented when possible, 
inasmuch as to break a satisfactory 
steam-joint is a thing which is to be 
avoided. It is by no means difficult 
to transfer the motion of the valve 
to reference-points outside of the 
valve-chest so as to avoid the 
This is easily done by means of a 




Fig. 576 



necessity for getting into the chest, 
trammel as presented in Figs. 571 and 576. 

It will be apparent that if one end of the trammel is placed in a center- 
punch mark on the valve-chest at such a point as, for example, on the 
stuffing-box, the other end can be used to fix upon the valve-stem itself 
a point which shall indicate the position of the valve within. If the 
engine be turned over by hand so that the valve-stem is made to travel 
to the right, the trammel can be made to locate a point on the valve- 
stem in which the outer end of it fits when the valve is all the way over 
to the right (Fig. 576). If the engine be turned over further, so that 
the valve-stem slides to the left, the trammel locates a point on the stem 
which belongs to the extreme of the travel to the left. Half-way 
between these a point can be marked by a center-punch, and when the 
point of the trammel lies in that punch-mark, the valve is in its central 
position. The engine being located with its piston upon its dead-center, 
the eccentric can be sHd around until the valve is in its central position, 
and with the trammel in place the valve-stem can be moved through a 
distance, first, to bring the lap fine and line with the port edge, and, 
secondly, the further distance proper for the desired lead. As in para- 
graf 421, due regard must be had to direction of motion and to the 
possible reversal of connection by rock-shaft or otherwise. 



646 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

Another method of setting the valve without taking off the valve- 
chest lid or bonnet is to depend upon the regular pulsations of the 
exhaust, as they furnish an indication to the ear. Their regularity in 
time indicates a symmetrical motion of the valve, and their regularity 
in intensity or volume indicates admission of steam and expansion 
symmetrically at the two ends. This is much the most sensitive method 
in two-cylinder engines with quartering cranks, as in the locomotive. 



CHAPTER XXVI. 

VALVE-GEARING. DESIGN. SPECIAL FORMS. 

435. The Zeuner Polar Diagram for Slide- Valve Design. The amount 
of port-opening, and the timing of the events in a valve motion which 
has been designed, can be laid down graphically from the motion of the 
driving-crank. The distance the valve has moved from its central 
position is the sine of the angle through which it has swept counted from 
the 90-degree point in a horizontal engine. (Figs. 577, 578, 579, 
Appendix) . 

A more convenient plan has been worked out by the late Professor 
Zeuner, which not only gives the facts for an existent gear, but can also 
be used in design to make the valve meet assigned conditions in advance. 
Modifications have also been made by other investigators. 

The basis of the Zeuner analysis is to compute the value for the distance which the 
valve has moved from its central or symmetrical position corresponding to any 
crank-angle, or when the main crank and valve-crank have moved through an angle 
CO. If r is the radius of the valve-crank, I and l^ the lengths of the valve-rod to the 
knuckle-joint and the valve-stem proper respectively, then from the diagram (Fig. 580) 




Fig. 580. 



in which the hne through X fixes the central position of the valve, the length BX may 
represent the space the valve has gone to the right for the angles d and w. If this 
distance be called z, then 

^ ^ BX = OB ~ OX. 

To find a value for OB: 

OB =0E + EB, + BB, 

= 0E + BB, + \/db;- - DE' 

= r sin (w + o) 4- ?! 4- \/J2 



— r- cos^ (w + o). 
647 



648 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

But ( Z ^j 1 = P — r^ cos2(w + ^) H ~ -. 

.-. OB = r sin (w + ^) + Z^ + Z ^^ -j 

when the last term is neglected as being so small a quantity as to be negligible. 
Similarly, a value for OX is 



2 ^ ' 2Z 

Combining these values and substituting, 

T^v t • / , ^x 1 7 , 7 r2 cos^ (w + o) r r^cos^^n 
5X = f = r sm (w + ^) + Zi + Z ^^ Mi + Z 21"""! 

= r sin (w + ^) + ^ fcos^ ^ - cos^ (w + ^) 1 

= r sin cos w + r cos 5 sin (a + F. 

If r sin = A 

and r cos d = B, 

$ = A cos w + 5 sin w + i^. 

F is a term to include the motion due to the angularity of the valve-rod. It is a 
small quantity, because the length Z is always great compared to r, and the cosines 
of the angles are small, and their squares smaller. The quantity F may therefore 
be dropped for convenience, or treated as a " missing quantity." 

The equation for $ will give also the value of the radius vector if a pole be taken 

in the circumference of a circle the co-ordinates of whose center (Fig. 581) are 

A B 

OB = a = — and BC = b = -^ , and whose diameter is r. For if P^ be any point 

whose radius vector is OPg and the angle MOP = w, then if 

OM = $ cos w, 

and 

MP = ? sin w, 

it can be proved that 

cm + NP^ = CP' = (^\\ 

{OM - OBy + (MP - MNy = /^y, 

(f cos CO — ay + (6 sin w — 6)2 "" ( 2 ) ' 
^ cos^ w — 2af cos w + a^ 4- ?2 sin2 ^^ _ 2b^ sin w -f- 6^ = / J ^ 

^ (cos^ w + sin^ oj) = 2 (a cos w + 6 sin w), 

whence 

<f = 2a cos w + 26 sin"a> ; 

and if 2a = A and 2b = By 

^ = A cos w + B sin w. 



VALVE-GEARING. DESIGN. SPECIAL FORMS 



649 



Or in other words, the motion of the valve from its central position may be represented 
by, or replaced by, the length of the radius vector of a polar circle whose diameter 
is the throw of the valve. The radius vector when w is zero determines the angle 

P3OR, because the main crank being at 
^R its dead-center the valve should have a 

radius vector equal to the sum of the lap 

and the lead. 



436. Graphical Solution by the 
Zeuner Polar Diagram. The equa- 
tions of the Zeuner analysis are 
practically never used, but the solu- 
tion is always found graphically by 
drawing the necessary circles full 
size. In Figs. 582 and 583 the 
radius ON is the throw of the 
valve, equal to the eccentricity of 
the eccentric. If there is no lap, 
the value of the radius vector is 
zero at the dead-center. Hence 




Fig. 581. 



for a horizontal engine, the posi- 
tion of the valve-circle with a diameter equal to the throw will be 
that of Fig. 582. When there is a lap, then the valve will be a distance 
from its central position equal to that lap when it is just ready to open 




Fig. 582. 



Fig. 583. 



the port. The distance OX in Fig. 583 will be the polar radius vector 
in this case, and it is apparent that the valve-crank should be 90 degrees 
plus an angle whose sine is the lap ahead of the main engine-crank; 
hence OX will be the lap and OB the required angular advance. If the 



650 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



engine has lead as well as lap, the valve must be distant from its central 
position a distance equal to the sum of the lap and the lead. The radius 
vector at the dead-center must then have a value represented by Oy 
when xy is the lead (Fig. 584). 

In these illustrations the engine-crank is to be assumed as belonging 
to a horizontal engine on its inner dead-center, and the rotation to be 
opposite in direction to that of the hands of a clock. The maximum 
throw is reached when the crank of the engine is in the position OB, 
and beyond this angle the valve starts to come back and close the 
admission. The closure of admission will occur when the valve on its 
return towards its central position is distant from it a length equal to 

the lap (paragrafs 85 and 86); 
hence if with as a center and 
with Ox as a radius a circle be 
drawn, it will intersect the circle 
whose diameter OB equals the 
throw, and which is called the 
A valve-circle, at points which will 
indicate the angles at which the 
valve begins to open and at which 
it closes. The radius drawn 
through Z (Fig. 584) gives the 
crank-angle at which the inlet- 
valve opens, and a radius drawn 
through W gives the crank-angle 
at which admission ceases or the cut-off takes place. It is obvious 
that in a valve with lead the valve would open before the piston 
reaches its dead-center. 

A strict adherence to the Zeuner method would have the circle 
described on OB conceived as attached to the engine-shaft, and the 
crank when at its dead-center to lie in the position ON. It is so much 
easier to cause the radius to swing through equal angles in the contrary 
direction, while the valve-circle remains fixed, that this method is 
preferred for practical use. 

If the diameter 50 be produced beyond to C, and a second circle 
of equal diameter be drawn upon OC as such diameter, a circle is given 
whose radius vectors give the exhaust events. If there is no inside lap, 
the exhaust opens and shuts when the radius vector of this second circle 
is zero, which is the position when the crank is at OP and OQ (Fig. 587). 
If there is an inside lap, the port will not open until the valve has moved 
through that lap. Hence the effective opening will begin only when 
the radius vector for the secondary circle exceeds the lap. Therefore 




Fig. 584. 



VALVE-GEARING. DESIGN. SPECIAL FORMS 



651 



if wdth as a center and inside lap Or as a radius a circle be drawn, its 
intersections with the secondary circle mil give the crank-angle at which 
the exhaust on the working-stroke and compression on the exhaust- 
stroke begin. 

437. Use of the Zeuner Polar Diagram. The Zeuner polar diagram 
not only gives all information which is given by a motion-curve, but 
it furthermore enables the user to design the valve and seat to fulfill 
specified conditions. In Fig. 584 the throw lap and lead are the given 
data. The angle AOB shows the advance of the eccentric disk beyond 
90 degrees proper for such lap and lead, and the cut-off takes place at 




Fig. 585. 



an angle AOP from the beginning of the stroke at dead-center. The 
design of a valve and its seat proper for the conditions assumed ^dll 
give a drawing such as Fig. 585. 

It is desirable that the valve in sliding upon its seat should come to 
the edge of it in its extreme throw, in order that the wear of the valve 
and seat may be uniform all over their surfaces of contact. Starting, 
therefore, at the point 0, which marks the extreme edge of the seat, a 
distance OB is laid off equal to the throw OB (Fig. 584), which is the 
radius of the valve-crank, and the maximum distance it can throw from 
its central position. The point B will be the beginning of the valve, 
since it projects over the port a distance Ox equal to BW and equal to 
the lap, and consequently at the point Z in Fig. 585 the outer edge of 
the port should begin. With the assumed throw of the valve and the 
assumed lap the port can never be opened wider than the distance vB 
in Fig. 584. Hence the indicated size for the port WP, Fig. 585, is the 
length vB in Fig. 584. If the port were made larger, the throw chosen 
would not open it wide, since BP equals OB; and if WP were less than 
vB, the valve in shding would go beyond the point P, which is unneces- 
sary. The calculation or design must be checked at this point to ascer- 
tain whether the area of the port -opening given by the product of W P 
multiplied by the permissible length in the direction perpendicular 
to WP gives an area sufficient or unnecessarily large to admit the 



652 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

quantity of steam required in the cylinder per stroke according to the 
calculation made in paragraf 236. 

A valve having no inside lap will have the inner edge of its working 
face which is the beginning of the exhaust-hollow line and line with the 
edge W of the port. If there is an inside lap, represented by Ov in 
Fig. 584, it will give a projection of the valve-face beyond the port- 
edge P. 

The steam-port must be separated from the exhaust-port by a parti- 
tion. The amount of metal in this partition is immaterial provided only 
it is enough to secure stiffness. It is often one-half the port width PW 
or vB, when there is no reason for making it anything else. The only 
effect of metal in this bridge or partition is to lengthen the valve and 
increase the power required to slide it on its seat (paragraf 445). 

The inner edge of the exhaust-hollow travels to the right or left a 
distance equal to OB, or the throw of the valve. It is desirable that 
when it is moved all the way to the right the hollow face shall still leave 
between its edge and the point or line V a space TV, equal to or larger 
than the port PW, discharging into that hollow from the right-hand 
port. That is, the motion of the valve to T should not constrict or 
reduce the passage through which the exhaust is escaping any further 
than it is necessarily reduced by the fixed opening corresponding to PW. 
This fixes the right-hand edge of the exhaust port in the seat, and the 
rest of the valve and seat is made symmetrical with the left-hand half 
already constructed. 

438. Valve-gear Problems and Design. It is beyond the present 
purpose to follow the use of the Zeuner valve-diagram further. It can 
be made to solve problems covering all quantities when a few assump- 
tions or data are made or given. The point of cut-off is one of the most 
usual data, as the engineer in most cases desires to work his steam with 
a certain expansion. The lead is another fundamental assumption. 
But a variety of combinations is possible involving the throw of the 
valve, the port-opening for a certain position of the crank, the release 
and the compression; and for these the student is referred to special 
treatises. 

For the immediate purpose in hand, however, the special problem 
will be considered in which the throw, point of cut-off, and lead are 
given and it is required to find the angular advance and lap to fill the 
condition assumed. 

In Fig. 586 let the horizontal line AB represent the whole travel of 
the valve in a horizontal engine. Bisect the line at and with OA 
as radius describe a circle on AB as diameter. Draw the radius OC, 
representing the angle from B as dead-center at which it is proposed to 



VALVE-GEARING. DESIGN. SPECIAL FORMS 



653 



have the cut-off take place. This is the point of closure of the valve; 
and since there is to be a lead, the valve should open before the crank 
reaches the position OB. The amount of angular motion before the 
crank reaches OB should be that through which the center of the crank 
shoiild move in subtending an angle measured by that lead. If, there- 
fore, with 5 as a center and the radius Bl equal to the assumed lead, a 
circle be drawn, the radius OD will give the position at which the valve 
crank stands when the port just begins to open. The maximum radius 
vector will be at a point half-way between these two crank-positions 
OD 'and OC, so that if the angle DOC is bisected by any of the 
usual geometric methods and the position OE thus determined, the 





Fig. 586 



Fig. 587. 



angle HOE will be the angular advance ahead of 90 degrees at 
which the valve-crank should stand. The length OX cut off from 
the line OC by the valve-circle just drawn is the value of the radius 
vector, or distance of the valve from its central position, when the 
steam-edge coming back over the port cuts off admission. OX is 
therefore the value of the lap, and a circle drawn with as centre 
and OX as radius will be the lap-circle for that diagram. It is a 
matter of simple geometric proof to show by similar triangles that 
the length yz, which represents the lead in its customary position, is 
the same as the length Bl used as an expedient in construction. 

439. Limitations of the Single Slide-valve. The cheapness, con- 
venience, simplicity, and permanency of the single slide-valve are the 
great inducements to its use. It can be shown, however, by the 
method pursued in paragraf 438 that the limit of expansive working 
with a single valve performing all functions is reached before it is 
demanded that these be cut off at half-stroke. If the conditions of 



654 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

cut-off at half-stroke be imposed and the method of paragraph 438 be 
followed, it must be apparent from Fig. 587 that the angle HOE will be 
a little greater than 45 degrees if there is a lead, and will be 45 degrees if 
there is none. The drawing of the circle of the lap with a radius OX 
determined by that valve-circle will give a lap so large in relation to the 
throw H that the port-opening becomes absurdly small. 

The matter is not materially helped by increasing the throw, because 
the lap increases with the throw. 

Furthermore, if there is no inside lap, the exhaust-opening and closure 
will take place at angles represented by the Hues OP and OQ, which, it 
will be seen, are 45 degrees from the crank-position which belongs to the 
ends of the stroke. The exhaust events have thus become distorted so 
that successful working becomes impossible. Hence with high expan- 
sion, secured by the expedient of increasing the angular advance of the 
valve-crank, the limit is certainly reached before two expansions are 
secured. A much higher degree of expansion is desired in all fly-wheel 
engines. How shall it be secured? 

440. Valve-gear for High Degrees of Expansion. Two-valve 
Systems. The advantages of the single valve induce an effort to make 
use of it if possible. Particularly in such mechanisms as that of the 
locomotive and the marine engine, where complication is to be avoided, 
it is desirable to retain the single slide. 

(1) The first method is to design the engine or its gear so that, as it 
is desired to cut off earlier, the throw of the valve should be lessened. 
It will be apparent that if the throw were equal to the lap or less than 
it, the valve would not move from its central position far enough to 
uncover either port. This makes the cut-off before the stroke begins, 
and is the limit. If a port of extra width or length will give area 
sufficient to let steam through in sufficient quantities to give the engine 
the necessary power, the admission will stop earlier and earlier as the 
throw diminishes; but, the angular advance remaining constant, the 
exhaust-ports open and close at the required angle for which they were 
designed. This principle underhes many designs of automatic cut-off 
engines, in which the governor varies the throw of the valve as the 
speed varies. It is also one of the underlying features of the link-motion 
used as a cut-off gear on locomotives, 

(2) The second method to secure high expansion is to use two shde- 
valves. These may work in the same valve-chest or in different valve- 
chests. When the two valves work in the same valve-chest it is usual 
to have them operated by separate eccentrics, and to divide the functions 
of distribution between them. The valve nearest the seat will control 
the exhaust-port openings entirely, and will be driven by an eccentric 



VALVE-GEARING. DESIGNS. SPECIAL FORMS 



655 



^l 



having a comparatively small angular advance. This principal valve 
will be called the main, or distribution, valve. The second valve will 
be driven by its own eccentric, set at a considerable angular advance, 
and will have no exhaust functions. Its business will be solely to cut off 

admission of steam into the ports or 
passages through the main valve 
whereby steam is admitted to the 
ports in the seat (Fig. 588). This 
valve will be called the cut-off valve, 
and from the fact that it slides or rides 
in the' back of the main valve this 
arrangement is often called the riding 
cut-off. The main valve requires to be 
prolonged so as to form the seat and 
port for the cut-off valve. The inner 
edge of this port performs cut-off 
functions late in the stroke, and pre- 
vents the cut-off valve from opening 
by its return motion the port which 
its greater angular advance has caused 
it to close. This riding cut-off arrange- 
ment lends itself easily to automatic 
adjustment of cut-off, since the release 
and compression are provided for at 
fixed points by the lower or main 
valve, and admission can be varied 
withifi very wide limits without affecting these exhaust functions. 
It may be a solid block, or in two separate blocks adjustable on their 
rod, as in the type of Meyer 
valve selected in Fig. 588. 

A modification of this 
system has a partition be- 
tween the two valves, with 
one or two rectangular open- 
ings in it (Fig. 589). Steam 
from the boiler passes to the 
main valve below the par- 
tition when the cut-off valve 

uncovers the opening. The objection to this arrangement is that 
the steam which surrounds the main valve partakes of the expansion 
after the admission is cut off by the upper valve, and the work of such 
expanding steam is lost. In the riding cut-off, to diminish this loss as 




Fig. 588. 




Fig. 589. 



656 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

far as possible, the thickness or height of the main valve is kept as small 
as consistent with giving the exhaust-hollow the depth which it requires. 
The small port 6 is a hand opening, or by-pass, to let steam enter the 




Fig. 590. 



main valve-chest if the engine shall have stopped with the upper port 
closed. 

When two valves are used in separate chests, the exhaust functions 
belong to one and the steam functions to the other. This makes both 
design and variation of cut-off exceedingly simple. Fig. 590, showing a 



VALVE-GEARING. DESIGN. SPECIAL FORMS 657 

section of the Porter-Allen engine, presents the features of a valve- 
gear of this sort in which the two valve-chests are on opposite sides of 
the cylinder and both are slide-valves. It will be easily seen from 
paragrafs 436 to 438 that the steam-valve need be planned only for 
lead, lap, and throw, and the exhaust-valve for throw and lap, when 
compression and release are fixed. 

441. Three and Four-valve Gears. When the principle of one valve 
has been abandoned it becomes very simple to design valve-gearing with 
a steam-valve for each end and an exhaust-valve for both ends, making 
a three- valve engine, or a separate valve for steam and exhaust at each 
end, making the four-valve engine (paragraf 418). In both the three 
and the four-valve engine the same advantages are derived, having the 
compression and release occur at fixed points in the stroke, while the 
cut-off and expansion can be varied automatically or by hand without 
interfering with the exhaust functions. The forms taken by the three 
and four-valve systems present almost every combination of lifting and 
sliding-valves which can be made. The typical river-boat engine, the 
older blowing-engines, and the older beam-pumping engines illustrate 
types of lifting-valves, and the Corliss engine and its imitators illustrate 
the cyhndrical sliding-valve to accompUsh these same results. 

442. Shortening Steam-passages. In the typical slide-valve which 
has been discussed hitherto the valve has been considered as short as con- 
sistent with adequate area for ports and for the exhaust-hollow. This 
results in engines of long stroke in a considerable length from the port at 
the valve-seat to the end of the cyhnder. As a rule in this design the 
valve is in the middle of the length of the cylinder, although this is not 
necessary if it be more convenient to have one passage longer than the 
other. The objections to the long passages from the valve-seat are: 

1. The friction which they oppose to the passage of the steam. 
These passages are usually moulded in the cylinder-casting by means of 
cores of proper shape, and their surfaces will be rough. The effect of 
this friction is to increase the difference of pressure which exists in th-e 
boiler or valve-chest and in the cyhnder. 

2. The long passage cools the steam by contact with its sides. This 
cooling is first by ordinary radiation, but more important than this is 
the cooling which follows when the passage is in communication with 
the exhaust-port. The lower-pressure steam, carrying perhaps a mist 
of watery particles, will absorb heat very rapidly during that part of the 
stroke in which it is serving as an exhaust-passage. The longer the 
surface the more heat will be required from the entering steam on 
the next stroke to heat the metal up to the temperature of the enter- 
ing steam. 



658 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

As has been heretofore observed, there is no difficulty in lengthening 
the valve and thereby shortening the passage. The size of the 
exhaust-hollow and the bridges which separate the ports produce no 
effect upon the distribution. The only objection is that increased 
length of valve gives an increased area for pressure, and consequently 
makes the valve demand more power to move it. In early designs for 
low-pressure steam, where this matter was of little moment, engines with 
very long sUde-valves will be found. They have been sometimes called 
Murdoch's valves. With high-pressure steam the difficulty has been 
met in another vv^ay. When the single eccentric is to drive a valve 




Fig. 591. 



performing all valve-functions the usual plan is presented in Fig. 591. 
It will be observed that while the valve acts as one it is really made in 
two parts, or like a B valve. The exhaust-port is divided by its special 
bridge, and the admission of steam is controlled by the left-hand edge 
of the left half of the valve and by the right edge of the right-hand half. 
The length of passage is thrown into the exhaust, where it makes no 
difference, and the length of the steam-port at each end is reduced to 
the shortest possible line. By joining the two halves by a rod sur- 
rounded by the steam in the chest there is no pressure on the valve 
between the active parts at each end. The system of Fig. 590 illus- 
trates the same short-port idea, and in the Corliss valves of Fig. 562 
the minimum port surface is secured. This same result is sometimes 
attained by making the valve resemble a low and broad letter H in plan. 
The uprights of the H are the working-parts of the valve, and the cross- 
bar between is made hollow and fits the exhaust-port, whose length is 
at right angles to the length of the steam-ports (Fig. 592). Cat-off 
valves which ride on the back of the main valve can be designed 
this way. 

443. Shortening the Throw of the Valve. Allen Valve. Another 
expedient for diminishing the power absorbed by an engine in working 
its own valves has been to shorten the throw or travel of the valve upon 



VALVE-GEARING. DESIGN. SPECIAL FORMS. 



659 



its seat. This must be done without constricting the port-area, which 
is an essential condition. If by keeping the throw of the eccentric 
larger than the throw of the 
valve, there is yet opened an 
equal port-area with such re- 
duced throw, there has been 
given to the eccentric a mechani- 
cal advantage to overcome the 
pressure which holds the valve 
at its seat. Fig. 593 shows the 
Allen slide-valve whose charac- 
teristic is the passage or hollow 
through the shell over the 
exhaust-port, and the use of a 
comparatively short seat or a 
seat with more than three ports 
in it. From the construction 
and the proportions it will be 
seen that when the steam-edge 
of the valve uncovers the left- 
hand port by a motion of the 
valve from its central position, 
the hollow in the shell is by 
that same motion brought into 
communication with the steam- 
pressure at the other end of the 
valve. In consequence of this a 
given motion opens twice as much port for the passage of steam into the 
cylinder as would be the case in the ordinary valve. Steam-pressure 
is thus very rapidly established as the valve moves a less distance than 
the port width which it is made to serve. This double ported principle 
will be seen also in Figs. 562, 602, 607. 

444. Gridiron Slide-valve. It will be immediately apparent that if 
the slide-valve be constructed with alternate holes and solid bars each 
of one inch in width which match similar holes and bars in the seat, 
that the motion of one inch which brings the holes in the valve to match 
the holes in the seat will open an area of port as many times one inch 
in the direction of motion as there are holes in either valve or seat. 
Fig. 595 shows a slide-valve of this construction, intended for steam 
only. It is called from its resemblance a gridiron slide-valve, and the 
principle of having many openings into the steam-passage gives it also 
the name of multiported valve. The adoption of this principle will be 




Fig. 692. 



660 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




Fig. 593. 



A^AI 



Fig. 596. 



^—fitr=^^^ 




Fig. 596. 



VALVE-GEARING. DESIGN. SPECIAL FORMS. 



661 



observed in many large engines, and is particularly useful for high 
pressures. 

Fig. 596 for example shows the very short-port passage and yet the 
large area for both steam and ex- 
haust in a four-valve engine in which 
the gridiron principle is applied. 
The valves can slide crosswise, due 
to their short travel, which results 
in a compact driving mechanism. 

The multiported valve-seat can 
also be made to serve another pur- 
pose, which will be understood from 
Fig. 597. The division in the port 
is carried all the way down to the 
bore, so that the piston in its move- 
ment towards the head of the cylin- 
der closes the inner port at either side 
before it reaches the end of the 
stroke. This inner port has been the 

principal dependence as an exhaust-port, so that when it is closed by 
the piston a very energetic compression is the result, and the piston is 
arrested by a cushion of the exhaust steam. On the steam end the 
admission is gradually cut off by the closure first of one port and then 
of the other. This principle of using the piston as a valve to close ports 
in the bore of the cylinder is the principle underlying several designs of 
so-called valveless engines. A modification of it is to be noted in 
Fig. 405. 




Fig. 597. 



CHAPTER XXVII. 

VALVE GEARING, BALANCED VALVES, CAM AND TRIP VALVE GEAR. 

445. Balancing Slide-valves. The power necessary to slide a valve 
upon its seat is measured by the area of the valve multiplied by the 
pressure upon that area, and by a factor expressing the coefficient of 
friction between the valve and its seat. The pressure is the net pressure 
or the algebraic sum of the downward pressure on the valve and the 
upward pressure exerted from the cylinder against the under side of 
the valve. It is not a difficult matter to make this calculation for 
assumed conditions. 

To evaluate the pressures to be balanced on a slide-valve, suppose a locomotive- 
valve 17 inches wide and 10| inches long, having a lap of 1 inch, a travel of 4 inches, 
a port of 14^ by 1^ inches, and an exhaust hollow of 6 X 14 J inches. Let the valve 
be working with the lever in the eight-inch notch, or cutting off at one-third stroke. 
The following areas and pressures will prevail: 

Port-area = 18 square inches (1) 

Exhaust-hollow = 87 square inches (2) 

Gauge-pressure = IGO lbs. per sq. inch (3) 

Back-pressure = 5 lbs, per sq. inch (4) 

Mean pressure = 110 lbs. per sq. inch . . . (5) 

Cushion-pressure = 40 lbs. per sq. inch (6) 

The downward pressure during admission, or one-third stroke, is exerted on 
10 X 17 = 170 square inches. 

After cut-off, during expansion, or two-third stroke, the whole area receives 
pressure = 10^ X 17 = 178 square inches. The average area or 174 square inches 
receives a downward pressure of 160 lbs. per square inch = 27,840 lbs., or nearly 
14 tons. 

Upward pressure from the cylinder relieves this somewhat. 

In the one third during admission (2) has (4) upon it = 435 lbs. 

" " second third, (1) has (5) upon it = 1980 " 

u u . .. ^2) " (4) •' - = 435 •' 

" >• third third (1) " (6) " " = 720 " 

" (1) " (5) •' " = 1980 •' 

Summation = 5550 lbs. 

or an average through the stroke of = 1850 ' 

Subtracting this from the average downward pressure 27,840 — 1850 = 25,990 lbs. 
net average downward pressure 

662 



VALVE GEARING 



663 



The work in foot-pounds per minute to slide the valve upon its seat 
will be the product of the pressure factor multiplied by the feet per 
minute through which this resistance to motion is overcome. It will 
be seen that the previous discussions have shown how these pressures 
may be kept as small as possible and how the motion or travel can be 
diminished. With high pressures and large volumes of cylinders to be 
filled steps must be taken to diminish pressure on the valve, since the 




Fig. 599. 



feet of travel must remain always a considerable quantity. The most 
satisfactory method for accomplishing this result gives rise to what are 
called balanced valves. The most effective methods to secure this 
balancing may be grouped into: 

1. The Piston Valve System. 

2. The Pressure Plate System. 

3. Counter Pressure Systems. 

In both the latter are several sub-divisions. In the last are the 
balanced poppet systems. 

446. Piston-Valves. The simplest form of balanced-valve is what is 
called the piston-valve, which is shown in the section of the valve and 
chest in Figs. 599 and 510. The piston-valve consists of an ordinary 
shell or D valve, which has been made to revolve around its valve-stem 
as a center so as to generate a volume of revolution. The plane faces 



664 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

of the typical slide-valve become the surfaces of a cyhnder, and the 
plane valve-seat must become a hollow cylinder which the valve-faces 
fit hke a piston. By referring to Fig. 600 it will be apparent that 
steam-pressure is equaHzed upon the two end-faces of the cyUndrical 
valve, and the contact of the valve with its bore prevents any pressure 
other than friction from getting at the valve sidewise. The only resist- 
ance to the motion of such a valve is its own friction, no matter how 
great the steam-pressure may be. The valve may be arranged with 
double pistons as in Fig. 510, or with single pistons as in Fig. 600. 




Fig. 600. 



The objections to the piston-valve are the difficulties from leakage and 
wear. The pistons cannot fit tight in their bore, because unequal 
expansion would cause them to be seized by the bore when the latter 
was cold and the pistons were hot. To prevent excessive leakage they 
must therefore be made steam-tight by means of spring-rings whose 
elasticity causes them to spring out against the bore while they fit 
grooves in the piston tightly enough to prevent leakage around them 
(paragraf 381). These spring-rings must be prevented from catching 
in the ports over which they slide by bridges of metal which prevent 
their enlargement when the rings are opposite the ports. These rings, 
however, cause friction and wear. When the piston-valve is used 
without rings great care must be taken to prevent the possibility of 
difference of temperature between the piston and its bore. Unequal 



VALVE GEARING 



665 



expansion would cause the piston to be cramped by the bore, and 
this must be prevented by jacketing the latter with extreme care. 
Fig. 600 shows this precaution taken. The piston-valve precludes 
great reduction of the clearances and the shortening of the passages. 
For very large marine engines, in order to diminish the diameter of the 
valves and at the same time to shorten certain connections, two sets of 
piston-valves are used, working together from a common valve-rod. 
The piston- valve is extensively used on locomotives, steam-hammers, 
rock-drills, and the like. Its great advantage for steam-hammer practice 
in large sizes comes from the ease with which the valve can be worked by 
hand. A favorite form of such piston-valves is rectangular or square 
instead of round. Round pistons are easier to make and to pack. 

447. Pressure-plate Systez^is. The pressure-plate system aims to 
secure the release of the valve from unbalanced steam-pressure by 




Fig. 601. 



receiving that pressure on a plate which is supported positively in the 
steam-chest and underneath which the valve shall slide. The principle 
is fundamentally the same as the piston- valve ; but the valve can be 
flat, and need only be steam-tight on its top and bottom, where it 
touches the seat and pressure-plates, respectively. 

The pressure will be on the ends equally; and the sides of the valve 
to be finished need only be the top and bottom, which slide on the seat 
and the lower face of the pressure-plate. The valve is a flat block, and 
its faces can be scraped true. Clearances are diminished and the 
lengths of the passages. The system will be found in very extensive 
use (Fig. 601). 



666 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

There are three great systems of arrangingthe pressure-plate principle. 
First, the fixed plate, non-adjustable. In this design the fixed plate 
rests upon lugs or ledges in the sides of the steam-chest or on its bottom, 




Fig. 602. 



the length -of the plate being such that the valve will always remain 
under it as it travels (Fig. 602 and right hand of Fig. 604); or the 
plate may be the top of the steam-chest. The valve may have, no 




Fig. 603. 



packing provision as in Fig. 602, or an adjustment may be provided 
as follows: To the back or top of the valve is fitted a spring-ring or 
an equivalent device, which fits the valve and the plate in such a way 



1 



VALVE-GEARING 



667 



that no steam can reach the top of the valve by reason of the contact 
continuously made between the valve and the plate through the spring- 
ring. It will thus be seen that the valve is in equilibrium of steam- 
pressures all around it except on its back, and the only resistance to 
its 'motion is the friction caused by the elasticity of the packing device. 
It is frequently arranged to have the space inclosed by the packing- 
ring communicate with the exhaust through a hole, so that if the 
packing-ring should leak, the leakage w^ould be into the exhaust-pipe, 
and it would be impossible for pressure to get upon the valve. Fig. 603 
shows the balanced valve of this fixed pressure-plate and adjustable- 
ring type. The design chosen for exhibition is one which has been 




Fig. 604. 



much used in locomotive service. In Fig. 602 the pressure-plate has 
relief-valves on its back which can open by excess of pressure from 
below, due to water forced back from the cylinder through the extra 
length of the ports. The piston-valve and the inelastic pressure-plate 
do not allow this displacement of the valve by excess of upward pres- 
sure. In Fig. 601 the pressure plate is held down upon its fixed 
supports by springs in addition to the steam-pressure, so as not to 
lift and clatter when steam is shut off. 

The second type of pressure-plate systems is shown at the left hand of 
Fig. 604. In this design the valve is a soUd block, but the pressure- 
plate which fits upon its back is arranged to be supported upon two 



668 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

inclined planes. The pressure-plate is also made to slope at the same 
angle so that by means of the adjusting-screw the inclined planes are 
made to sHde over each other; the surface which bears on the valve 
remains always parallel to itself. It will be apparent that any desired 




Fig. 605. 



pressure of contact can be ma'de between the sliding-valve and the 
pressure-plate while the pressure of steam is kept from the back of the 
valve. 

In Fig. 598 A in the appendix is another form of adjustable pressure- 
plate, adjusting lengthwise. Or, again, the pressure-plate may bear 
upon flat surfaces, from which it is held away by packing-strips, which 
are taken away as wear may render this course necessary (Fig. 605), or 
for exhaust-valves the construction of the right hand of Fig. 604 may 
be used, where the pressure-plate is bolted in place, and is relieved by 
surfacing anew as it wears. 

The third pressure-plate system has been adopted for rougher grades 
of work than the two preceding. The pressure-plate is a disk or plate 
of steel or similar flexible and resilient metal. It is so calculated that the 
pressure upon it shall force it down upon the valve which slides under it, 
but its resistance to such flexure shall be sufficient to permit only the 
desired nip or squeeze to reach the valve and prevent leakage of pres- 



VALVE GEARING 



669 



sure between the valve and the plate (Fig. 606). In some old designs 

this flexible pressure-plate was supported at its central point by a stud 

which came up through the top of the steam-chest, and 

could be adjusted from outside with steam upon the 

valve within. 

The first two systems are the most usual. 
448. Valves taking Steam Internally. Closely re- 
sembhng the piston-valve and pressure-plate modifica- 
tions of it is the third type of balanced valves. In 
these, provision is made to have the upward pressure 
exerted by the steam upon the area made just enough 
less than the area exposed to downward pressure so as 
not to hft the valve. The unbalanced force tends to 
keep the valve upon its seat. This compels the use 
of a hollow valve whose upper side shall either fit 
against a surface, adjustable or fixed, which shall 
serve to keep pressure away from the outside of the hollow valve on 
the side corresponding and opposite to its seat, or a scheme is used 
in which the pressure is balanced around it (Fig. 607). Here it will be 
observed that the steam enters within the hollow valve from below 
and presses upward over the under side of the shell. This would lift 
the valve away from contact with the seat were it not for the 




Fig. 606. 




unbalanced pressure in the Allen thoroughfares over the two exhaust 
ports. This is practically a hollow piston-valve, with pressure inverted.. 
These types run naturally into the pressure-plate system with steam 
on the ends only. 

449. Valves with Counter-pressure. A very simple arrangement of 
counterbalance was applied to many Worthington pumping-engines of 



670 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

large size. The valve was attached by a link and pin-joints to a piston. 
This piston fitted a vertical cylinder directly over the valve, the area of 
the piston being so calculated that it was not quite enough to lift the 
valve even when the latter had its maximum pressure underneath it. 
The cylinder needs only to be long enough to permit the swing-link to 
follow the valve as it moves back and forth. This principle of counter- 
poising pressure by means of a piston has also been used in massive 
vertical engines to provide for the weight of the valves and their rods 
and to keep the strain always in one direction. It can also be similarly 
used to counterbalance the weight of the mechanism of the engine 
itself. 

Locomotives have been fitted with a nest of rollers which lie in a 
groove below the surface on each side of the valve. They come just 
to the level of the seat, and carry the downward pressure to a degree 
without allowing leakage below the valve and between it and its seat. 
They form a roller-bearing. 

450. Poppet-valves. It is one of the great advantages of the double- 
seated lifting- valves that they are nearly, if not entirely, balanced, as 
discussed under paragraf 416. Their limitation when massive to low 
rotative speeds has restricted their use as a means of reheving the 
pressures to be overcome at high speeds of rotation. 

451. Cam Valve-gears. The convenience of a cam as a means to 
operate the valve distributing steam to the engine-cylinder was early 
appreciated. The profile of the cam, whether revolving continuously 
or vibrating through an arc or a part of a circle, can be designed to give 
to the valve exactly the desired motions and at the desired times. It can 
moreover hold the valve open or shut while continuous motion of other 
elements or organs is in progress, which the crank motion does not 
permit; and furthermore it permits the sudden or 
rapid closure of the valve by gravity or by a spring 
when the profile of the cam lets go of the stem. 

Cam-motions are of two great classes. In the 
first the cam-shaft revolves continuously in one 
direction. In the second the cam-shaft is a rock- 
shaft vibrating through an angle first in one direc- 
tion and then in the other. In cam valve-gears of 
the first class there are two arrangements usual. In 
the first arrangement the cam bears against a roller 
in contact with its exterior surface; such are 
called outside cams (Fig. 608). The roller is conveniently mounted 
in the end of the valve-stem, and can be in the plane of such 
valve-stem, or the cam may bear against the end of a pivoted lever 




VALVE-GEARING 



fi71 



which actuates the stem (Fig. 610). In the other arrangement the 
roller fits in a groove in the side of a cam-plate. 

The outside cam-motion works the valve in one direction only; for 
the return motion either gravity or a spring must be depended on, or 
else there must be a roller or yoke opposite to the first one to bring the 

rod back with a motion 
similar to that caused by 
the cam against the first 
roller. This outside cam 
arrangement has the advan- 
tage that the roller always 
turns in the same direction. 
The two-roller or yoke-plan 
has a grave objection from 
the difficulty that wear 
prevents the distance be- 
tween the roller or yoke 
surfaces remaining always 
the same as the net diameter of the cam at every point. If the roller 
or yoke does not touch the cam continuously, there is a jar and shock 
followed by wear at the points where such contact begins. 

The side-cam arrangement where the roller fits in a groove has the 




Fig. 609. 




Fig. 610. 



entire motion of the valve effected by that one roller and groove. This 
is called the box-cam system. The difficulty is that the inside surface 
of the groove drives the roller on the Hfting stroke, and the outside 



672 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

surface of the groove drives the roller on the reverse stroke. Hence at 
each reversal of motion the rotation of the roller must be instantly 
reversed, and the inertia of the roller resisting this reversal prevents 
perfect roUing contact at those points of reversal, and wear and rattle 
ensue. The difficulties from the inertia of the rollers and the mass of 
the valve-rods have limited in the past the use of cams to relatively low 
rotative speeds. Recently a design has been brought forward in which 
the reverse motion of the valve-stem is caused by a pressure of air or 
steam upon a piston on the rod, so that the mass to be moved by the 
cam is reduced to its lowest terms, and the pressure on all pin-joints is 
kept constantly in one direction (Fig. 613). 

When the cam rocks or vibrates upon an oscillating shaft instead of 
revolving continuously (Fig. 610) it drives in one direction only, and the 
weight of the rod or a spring, or both, must be used to return the valve. 
This rocking or oscillating cam is almost a distinctive peculiarity of 
the beam-engines used in deep-river-boat practice of Eastern America 
(Fig. 389). These are four- valve engines, the two exhaust-valves being 
on the right-hand side and the two steam-valves on the left, as the 
observer faces the engine (Fig. 561). Eccentrics on the water-wheel 
shaft transmit a reciprocating motion to cranks upon a rock-shaft which 
crosses the front of the engine and is divided into two sections at the 
middle bearing. The valve-rods are lifted by the profiles of curved cams 
or wipers which bear against the horizontal surfaces of toes which are 
lifted by the rocking of the rock-shaft. The exhaust-valves must be 
open full stroke, and consequently the plane of the two wipers has 
almost a common tangent at the dead-centers, so that the cam on one 
side will have just closed the valve at the upper end of the cylinder when 
the cam on the other is to open the valve at the lower end. The steam 
cams make an angle with each other, so that there will be an interval 
between the closing of one and the opening of the valve at the other end. 
This gives the interval for expansion at the end of each stroke, while 
securing admission at the proper point. The eccentric of the steam end 
of the rock-shaft is usually of greater throw than the exhaust side, so as 
to give greater amplitude to the motion of the cams, and the steam-cams 
are made longer than the exhaust-cams, in order to give gentle curves 
for their action, and yet open the valves quickly and close them promptly. 
This valve-motion of wipers and toes was first proposed by the Messrs. 
Stevens in 1848, and iS usually known as the Stevens cut-off. 

The rocking-cam also appears in Figs. 610 and 614 for actuating the 
valves of inclined cyHnders by bearing against the under side of a 
pivoted lever to which the poppet-valve is attached. 

The Western river-steamboat with horizontal engines for its water- 



VALVE GEARING 



673 



wheel usually operates its valves by continuously moving cams on the 
water-wheel shaft, which bear against the surfaces in a frame to which 
the revolving rod is attached. The relatively slow motion gives rise to 
no difficulty with this type of gear (Figs. 609, 614). 

Cam motions can be made adjustable or variable by arranging to have 





Fig. 611. 



the profile of the cam variable. This is usually done by having the 
cam made up of several layers which are movable under the roller in 
such a way that the acting face of the cam can be made shorter or longer 




Fig. 612. 



at the pleasure of the operator. Or the cam is made of a varying profile 
at different sections of its considerable face, and different parts are 
brought under the roller or valve-lever (Fig. 611). 



674 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

It is not often attempted in cam valve-gears to make one cam and 
one valve perform all the valve-functions. Cam valve-gears are usually 
three or four- valve designs. The cam gear is usually worked with 




Fig. 613. 



poppet-valves, because the valve must oppose the least resistance to 
motion, and must be balanced so as to be self-closing. Examples of 
cam valve-gear will be found in Figs. 609, 610, 613 and 614. Fig. 612 



VALVE GEARING 



675 



shows an arrangement which holds the valve open or shut through a 
considerable angle of the rotation of the shaft. 

452, Trip or Releasing Valve-gears. Belonging to the same general 
clas^ as the cam gears are those in which a detent or catch which is 
pushed or pulled to open the valve is released when the valve is to be 
closed, so that it returns to its closed position independent of the 
operating mechanism. This return is effected usually by a weight or a 
spring or both, so that the valve is closed more quickly than it could be 
if the connection of the valve to the operating mechanism were positive. 
This principle of trip or release gears is identified in America with the 




Fig. 614. 



name of Frederick E. Sickles (1841), but has received its greatest 
development under the name of Corliss (1849), with whose name it is 
best identified in Europe. The original Sickles cut-off was applied to 
poppet-valves lifted by cams. When the cam had lifted the valve- 
stem to the desired point, a latch connection between the stem and the 
lifting mechanism was released and the valve closed independently by 
dropping. As the hfting mechanism descended it displaced the latch 
or detent until it had passed the latter, when, by a spring, the latch 
came forward into position to be caught by the lifting mechanism Avhea 
it was to make its next stroke. As appUed to early engines the Sickles 
principle was arranged to have the latch release adjustable by hand. 
It becomes easy to have this adjustment made automatically by the 



676 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

governor, and this easy adaptation has been a great stimulus for the 
development of this class of valve-gear. A type of gear which presents 
the trip-and-release mechanism in its simplest form is that which is 
identified with the Greene engine, Fig. 615. It will be seen that the 
slide ./ traverses back and forth driven by an eccentric. This slide 
carries the latches GG\ which are held upwards by means of springs and 
are inclined upon their upper faces. It will be apparent that as the 
sharp corner of the latch catches the end of the arm B it will swing it 
upon one stroke, but will be depressed by it on the other. As soon as 
it has passed by, however, the spring under the latch will force it up 




so that it will be ready to catch and swing the arm B on the next stroke. 
If the governor mechanism be attached to the rod F, it is obvious that, 
if it acts to depress the latches G, the arm B moves the valve-stem D 
through a less angle, and lets it go so much the sooner. The exhaust- 
valves of the Greene engine are operated independently underneath the 
cylinder, one at each end. 

453. Corliss Valve-gears. The Corliss valve-gear involves four 
separate features. The first is the rocking cylindrical valve, of special 
construction to eliminate sticking fast by expansion. The second is 
the operation of both steam-valves and exhaust-valves from a rocking 
wrist-plate; the third is the trip or release of the steam- valves by the 
governor, and the fourth is the closure of the steam- valves by gravity 
or a spring. 

The Corliss system uses four valves, two of them for steam above the 
axis of the cylinder, and two for exhaust below. In the form shown in 



VALVE GEARING 



677 




Plan of Exhaust Valve 



Scale of Feet 



Fig. 616. 




Fig. 617. 



678 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

Figs. 562 and 616 they are made directly in the cylinder-heads. It is 
also quite usual to put them upon the sides, as shown in Fig. 563. The 
characteristic of the valve is that the spindle by which the valve is 
caused to rotate is not fastened to the valve, but is independent of it. 
This takes away the objection to the cylindrical cock-valve. The valve 
need not fit tight all about its casing, but must turn when its spindle is 
turned from without. On the type shown it will be apparent that ports 
and passages are of the smallest possible length and surface, thus taking 
advantage of the features discussed in paragraf 417. 

The second feature of the Corliss valve-gear is the operation of the 




Fig. 618. 



four valves from points on a wrist-plate which is made to vibrate back 
and forth through a considerable angle by its connection with the 
eccentric. The two upper .valves, Fig. 617, are connected near the verti- 
cal diameter of the wrist-plate, and the two lower or exhaust- valves 
connected nearer to the horizontal diameter. It will be apparent from 
this peculiarity that the steam- valves will be opened rapidly as the 
engine passes its dead-points, while the exhaust-valve will be held 
wide open during that fraction of the angular motion of the wrist-plate 
during which the link of the exhaust- valve is coming up into hne with 
the center of the wrist-plate and is passing beyond and above that line 
and is returning to its original position. The other steam and the 



VALVE GEARING 679 

other exhaust-valve are without effect on their openings during the 
stroke in which their mates are in action. The valves usually work in 
diagonal pairs. The wrist-plate appears in many forms in the various 
makes of engine. Fig. 618 shows a type where a larger throw is given 
to the steam-valves than to the exhaust-valves to extend the period 
during which cut-off may take place. The eccentric driving the wrist- 
plate will be 90° ahead of the crank so as to operate the exhaust valves 
at the right time. Since the trip can only take place during the push- 
ing stroke of the steam-rods, it cannot take place later than one-half 
or three-eighths stroke when the whole wrist-plate is driven by the one 
eccentric. This is the basis for two wrist-plates and two eccentrics, 
the steam-plate having much the larger throw and set at a different 
angular advance. By doing this the range of variability of the cut-off 
is much wider, without changing the form of the indicator card. 

The third feature of the Corliss gear is the release or trip of the steam- 
valve rods, by w^hich the hold of the wrist-plate upon the valve is 
dropped and the valve closed suddenly by weight or spring. The 
peculiarities of the method followed in the detail of this release-gear 
differentiates many of the various Corliss engines from each other. In 
the very earliest forms the detent was thrown off as the valve-rod moved 
up an inclined plane or wedge. Another form throws a cam or eccen- 
tric into engagement with a curved arm or toe, and the pressure of 
these upon each other forces the rod to let go of the catch on the arm 
of the valve. In all of these forms the adjustment of the gear is usually 
made by the governor, so that the speed of the engine varies the length 
of admission by causing the cut-off when the trip occurs. The exhaust- 
valves are positively connected to the wrist-plate so that release and 
compression are constant, while cut-off and expansion vary according 
to the work of the engine. Fig. 619 shows the trip mechanism and 
Fig. 607 shows the same parts. / is the valve-spindle, lifted by a hook 
or catch on F. G causes the release or trip, as controlled by the gov- 
ernor connected through the rods H. 

The fourth feature of the Corliss valve-gear is the closure of the 
valve by a weight or a spring with dash-pots. The dash-pot is a cylinder 
in which fits a piston nearly or entirely air-tight. (Fig. 617.) As the 
valve is lifted it lifts the piston in the dash-pot. Air enters below in 
the weighted dash-pot and when the valve is released the Aveight of the 
piston, with or without the help of additional weights, closes the valve, 
when the retarded escape of air in the dash-pot arrests the motion 
without excessive shock. In the vacuum dash-pot the piston fits 
tightly, and the lift of the piston, creating a partial vacuum below itself 
in the dash-pot, causes atmospheric pressure to become the weight or 



680 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



spring which closes the valve. The compression of the air remaining 
below the piston performs the cushioning necessary to prevent shock. 
454. Advantages of Trip Valve -gear. The advantages of the Corliss 
and other trip valve-gear are: 

1. The degree of expansion or the point of cut-off can be varied 
through a wide range of load variation while the release and com- 
pression are kept constant. 

2. Quick opening of inlet-valves establishes full boiler-pressure in 
the cylinder early in the stroke. It is a feature of most of these gears 



Cover; 



'^^^hJtod 




Fig. 619. 



that their construction and operation give large port-areas and little 
friction through the valves. 

3. The inlet-valve closes quickly. The effect of this is to increase 
the area of the work-diagram by giving a sharp corner at the point of 
cut-off instead of a rounded curve. A rounded corner at this point has 
the effect of gradually lowering the pressure from wire-drawing as a 
consequence of gradual closure. 

4. This type of gear, being specially adapted for engines which are 
designed to be regulated by varying admission, gives the advantage of 
making the terminal pressure low. 

5. The ease of adjustment of such independent valves if variation at 
the two ends of the cylinder should be desirable. 

6. The small motion and the period of rest for the steam-valves after 
closure diminish the friction of the valve-gear and the attendant loss 
of power. 



VALVE GEARING 681 

455. Disadvantages of Trip Valve-gear. The trip valve-gear, being 
almost always a multiple valve-gear, is open to the following objections: 

1. The compUcation and number of parts in most of the gears. 

2. The expense of most of the engines fitted with complicated gear. 

3. The limitation in rotative speed or number of revolutions imposed 
by the necessity of engaging the catches and valves. The inertia of 
the masses precludes an instantaneous action in response to the spring 
or weight, and the snap-and-catch action becomes noisy when the 
springs or similar devices have stiffness sufficient to make them positive 
at speeds faster than 150 revolutions per minute. 

4. The trip and the cam valve-gear have this objection in common, 
that the release of the catch and closure of the valve must be effected 
by the governor during that stroke of the valve-rod which nominally 
opens the valve. In other words, in a lifting-valve the release must 
take place before the valve reaches its point of greatest opening. This 
limits the range of the ordinary gears of this class with respect to their 
ability to adjust the point of cut-off, and is only remedied by the second 
wrist-plate and its attendant complication and cost. 

5. The variable stroke or traverse of the valve. The seat wears 
through the angle of most frequent motion more than beyond this 
range, and this forms shoulders which are hit by the valve on its wider 
swmg. 

456. Sundry Valve-gears. The method of operating the valves of a 
non-expansive engine by a steam-cylinder, which is used in direct-acting 
pumps and has been discussed in paragraf 149, should be referred to 
again in this connection. See also Fig. 697A in the Appendix for a 
riding cut-off valve thrown by steam. The cataract of the Cornish 
pumping engine is another system of valve operation. 



CHAPTER XXVIII. 

REVERSING VALVE-GEARS. LINK-MOTIONS. 

460. Reversing-gears with One Eccentric. It will be apparent from 
discussions in parts of Chapter XXV, which have treated of the setting 
of valves, that if the valve had neither lap nor lead, so that the angular 
advance of the valve-crank was 90 degrees ahead of the engine-crank in 
order to go forward, it could not be at the same time 90 degrees ahead 
of the same crank which was to turn backward. A very simple revers- 
ing-gear for a valve of this type can be made by having the valve-stem 
driven from a rocker-arm and so constructed that the rod of the eccentric 
can be geared to it either on the same side of its center of motion as the 
valve-stem or at will upon the opposite side. From the discussion in 
paragraf 421 it will be apparent that when the motion of the eccentric- 
rod is reversed by the rock-shaft the engine will turn in one direction, 
and when it is not so reversed it will turn in the other. When the valve 
has lap or lead or both, and is intended to work expansively, the valve- 
crank is 90° + an angle a, which represents the angle AOE in Fig. 584, 
ahead of the main crank. Hence the position of the center-lines of 
eccentrics for forward and backward motion will be distant from each 
other an angle represented by 180° — 2a, and a reversing motion by 
the method just described is impossible. 

There are two methods of reversing an engine using 'one eccentric. 
The first is to have the eccentric loose upon the shaft and free to move 
independently of that shaft between two stops which are bolted, keyed, 
or otherwise secured to the shaft. The loose eccentric has a corre- 
sponding lug or projection which engages with these stops. The angular 
distance between the stops upon the shaft is so adjusted that when the 
first one engages with the lug upon the eccentric-disk, the relation of 
the eccentric-crank to the main crank is that which adjusts the valve- 
gear to distribute steam for forward motion. The resistance of the 
valve as the engine turns in one direction keeps the lug and first stop 
continuously in contact. If the engine-shaft be turned in the opposite 
direction by operating its valves by hand, the first stop will leave 
contact with the lug, and the eccentric will stand still by reason of the 
friction of its attachments until the second stop on the shaft comes in 
contact with the lug on the eccentric. The adjustment of the second 

682 



REVERSING VALVE-GEARS. LINK-MOTIONS 683 

stop is such that when it touches the lug the relation between the 
eccentric and the main crank is that for distributing steam for back- 
ward motion. This arrangement of loose eccentric with lug and stops 
on the shaft has been a very favorite design for ferry-boat engines. The 
working of such boats in and out of slips is done by hand-working of 
the valves in any case, and their comparatively slow rotative speed 
and the large masses in the disks and rods lend themselves to this 
arrangement. 

The second single reversing-gear adjusts the eccentric through the 
angle 180° — 2a by having the latter borne upon a sleeve to which it is 
feathered, so tnat it must rotate with it and the shaft, while the sleeve 
can be slid lengthwise on the shaft under the eccentric. Tnis sliding 




Fig. 620. 




Fig. 62L 

of the sleeve is do.ne by a lever which has a latch attachment so that it 
can be locked in the desired position. The sleeve has a spiral slot cut 
in it, the slot subtending the angle of 180° — 2a and fitting a radial pin 
projecting from the shaft. It will be obvious that when the sleeve is 
slid lengthwise along the shaft the slot and pin will twist the sleeve 
through the angle 180° — 2a, and carry the eccentric through that 
same angle. The latch prevents readjustment except at the will of 
the runner. This makes a very compact reversing-gear, but is limited 
to engines of small size (Fig. 409). It is much used in small launches 
and in geared road-rollers or traction-engines. 

461. Reversing-gears with Two Eccentries. Gab-hooks. It makes 
so much simpler a reversing-gear to use two eccentrics, one set 90° + a 
ahead of the crank for forward motion, and the other set 90° + a 
behind it, which becomes that same angle ahead of the crank for back- 
ward motion, that this type of reversing-gear is much the most usual. 
There is a rod from each eccentric which is to be hooked and geared to 
the valve-stem at will, and the method of bringing the forward and 
backward eccentric-rod into gear with the valve-stem constitutes the 
differentiating feature of all forms of motions. 



684 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

The simplest and oldest device to attach the eccentric-rods to the 
valve-stem is a hook. This hook, called a gab or gab-hook, is simply a 
hole which fits a pin on the valve-stem or on a rocker-arm connecting 
to it, which hole has one side cut out and away so that it can be lowered 
down upon the pin or hfted off from it. Of course the two hooks must 
not be engaged with the same pin at once, and many different methods 
are used to take care of the hook and rod which for the time being are 
not to engage with the pin. The simplest is a hf ting-roller so adjusted 
that when brought against the under side of the rod it lifts it above the 
plane in which the pin travels. This may be done also by lifting a sus- 
pending-link. Other devices involve the use of cams or bars which 
shut down over the sides of the hook and fill up the hole, and are held 
in place by a latch or snap. With these the eccentric-rod may slide 
upon the pin itself, but when these appliances are in place the hook is 
closed and takes no hold of the pin. Figs. 620 and 621 present certain 
forms of gab-hooks. 

The objections to the gab-hook are three: 

1. The engine reversed by this means must have a low speed of rota- 
tion. 

2. The engine has to be of such a character that the reversal can be 
leisurely. It is not convenient to reverse at speed with a gab-hook, 
but the engine must be turning slowly when the hook is dropped upon 
the pin. 

3. The engine must be of such a character that it can be started by 
hand-working of its valves. The reason for this is that there is but one 
position of the main crank in which the hook of the forward gear and 
that of the backward gear coincide, so that either can be dropped upon 
the pin and operate the valve properly to pass from forward to back- 
ward motion. This position is the dead-center, either outward or 
inward, on which the engine-runner would never stop his engine if it 
could be helped, so that hand-starting is compulsory. 

To avoid the objections to the ordinary gab-hook so that the engine 
might be reversed at speed and started in the reverse direction without 
hand-working, the mouth of the hook was widened and the sides 
lengthened so that it took somewhat the shape of an inverted letter V. 
The distance apart of the horns of this V hook was made equal to the 
travel of the eccentric-rod plus the diameter of the pin, so that, no 
matter where in its course the pin might happen to be, the sides of the 
hook, pressed upon the pin, would slide it in the direction of motion until 
it caught into the hook proper at the foot of the V. These V hooks were 
early solutions of the problem of reversing the locomotive engine. 
Figs. 621 and 614 give the general" appearance of such hooks. 



REVERSING VALVE-GEARS. LINK-MOTIONS 



685 



463. Link-motion of Stephenson or Howe. The difficulties attend- 
ant upon large-size hook-gears for reversing when they came to be 
applied in high-speed practice brought about the development of what 
have been called the hnk-motions. If the forward and the backward 
hooli be made to face each other so that one hooks upon the pin from the 




top and the other from the bottom, and if these two hooks be joined 
together on their outer and inner edges by two arcs of circles struck 
from the center of the shaft, there will be derived the Stephenson link. 
The upper hook of the old gear becomes that part of the slot in the hnk 
just behind the joint of the forward eccentric-rod to the linkj and the 



686 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



lower hook the similar part of the link-slot behind the joint to the back- 
ward eccentric. The curved profile of the link keeps the two eccentrics 
from undesired motion, and the pin of the valve-stem fits in a suitable 
block in the slot of the link, so that the latter is always ready to be 
moved to bring either forward or backward eccentric to drive the valve, 
while the eccentric not required simply vibrates the link around its 
virtual center without affecting the valve. Fig. 622 shows the typical 
Stephenson link-rnotion as designed for locomotive practice and Fig. 623 
its skeleton diagram. There require to be attached to the link con- 




FiG. 623. 



venient connections to bring the forward or backward eccentric into 
line with the pin and to hold it at the desired position, but their con- 
struction requires no explanation. 

This simple form of reversing-gear was appHed to early locomotives 
turned out in England by Stephenson, but strong claims have been 
advanced by a William Howe for its first suggestion in 1843. 

463. Features of the Stephenson Link-motion. The Stephenson 
link-motion has certain peculiarities. If the valve had neither lap nor 
lead, so that the two eccentrics were 180° apart, it would be apparent 
that the link would vibrate around a virtual axis at its middle point, 
and that when the pin connected with the valve-stem coincided with 
that axis, the valve would have no motion. The angle between the 
eccentrics is not 180°, on account of lap and lead, and hence when both 
eccentrics are near the horizontal line in a horizontal engine they are 
each moving the link in the same direction at top and bottom. That 
motion, however, is usually so small that it does not uncover the laps 
over the port; or in other words, cut-off takes place before the stroke 
begins. At intermediate points above and below the center the travel 



REVERSING VALVE-GEARS. LINK-MOTIONS 



687 



of the valve is less than full throw of the eccentric, and by reference to 
Chapters XXVI and XXIX it will be apparent that earlier cut-off and 
greater expansion will be secured by this diminished throw, and yet 
without seriously distorting the exhaust events, since the angular 
advance is not disturbed. It is no disadvantage in locomotive practice 
to have compression increase with earlier cut-off. The heavy duty of 
the locomotive is in starting its load from rest, and at very high speeds 
on a level track the engine is doing much less work, so that it can be 
operated at earlier cut-off. The compression is a decided advantage 
at the high rotative speeds. It is the simpHcity of combining the 
variable cut-off gear (which is desirable) with the reversing-gear (which 
is necessary) and in one mechanism so simple as to be operated with 
one lever, which has given the Stephenson link-motion its popularity 
for the locomotive. 

The only theoretical objection to be urged against the Stephenson 
link is its slight inaccuracy, which produces a variation of the lead at 
different points of cut-off. By reason of the fact that the link is 
raised and lowered, carrying with it the rods, the latter are shifted 
around their eccentric disks. It will be seen that when the angle is 
varied which the eccentric rod makes with the line through the dead- 
center of the engine crank, from which angles are counted, there will be 
of necessity a motion of the valve at dead-centers of the engine-crank, 
since the effect produced is to diminish the angle 90° — a, which is 
therefore the same as increasing the angular 90° + a, which measures 
the angular advance ahead of the crank. To increase this angular 
advance ahead of the crank is a thing which is done where the lead is 
to be increased (paragraf 429). The lead, therefore, increases as the 
cut-off is made earlier. The following table shows the extent of these 
variations in a standard locomotive gear, especially when a little worn: 



Notch in 


Travel of 
Valve. 


Port-opening. 


Point of Cut-off. 


Point of Release. 




Sector of 
Lever. 


Forward. 


Back- 
ward. 


Forward. 


Back- 
ward. 


Forward. 


Back- 
ward. 


Lead. 


20 
19 
18 
16 
14 
12 
9 
8 


5 

^ 
4 

n 

2i 


H 
I 


i 


201 
19f 

m 

16i 

14 

12 

8 


20i 

m 

m 

16i 

14 

111 

61 


231 

2211 

22| 

21ii 

20ii 

19f 

181 

17 


23| 

22| 

22i 

21^ 

20^ 

19^ 

ISA 

16f 


1 
1 



The throw of the eccentrics v^^as 5 inches, the steam-ports 1^ inches and the 
exhaust-ports 2f inches wide. The lap was | of an inch outside and ^ inside. 



688 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

464. Gooch*s Link-motion. To counteract the difficulties of the 
Stephenson motion caused by shifting it around the eccentric and shaft, 
Sir Daniel Gooch, a railway motive-power engineer of England, reversed 
the Stephenson link and made the valve-stem pin sUde up and down 
in the Hnk which was suspended, so as to be unable to rise or fall 
(Fig. 190). It is obvious that the reversing and cut-off action are 




Fig. 624. 

retained, but the variation in the lead is eliminated. This motion has 
never been popular in America, since for its satisfactory working the 
valve-stem element HNF must have considerable length, and the 
design of American locomotives makes it difficult to secure this. If 
the curvature of the link has a short radius, irregularity in the valve- 
motion is introduced. 

465. Allan's Link-motion. The Allan link-motion combines the 
characteristic features of the Stephenson and Gooch. The link and 
valve-stem are swung from opposite ends of a lever pivoted at or near 
its center, and variation in position of the stem and link is produced by 
lifting one and lowering the other. The advantage of this form is the 
straight profile of the link, which makes it easy to machine in the shops, 
but, like the Gooch Hnk, it has never met much acceptance among 
American locomotive-builders, where the type of outside-cyHnder engine, 
which is preferred, makes it more usual to put the valve mechanism 
between the frames under the boiler. It has the advantage over the 
other two that the weight of link and of valve-stem partly balance each 
other so that counter-balancing weights or springs are not required as in 
the other forms. 

466. Radial Valve-gear. Joy's Valve-gear. Variations have been 
made upon the link-motion hitherto discussed in the effort to do away 



REVERSING VALVE-GEARS. LINK-MOTIONS 



689 



with one of the eccentrics or both. The eccentrics in fast-running 
engines are sources of friction by reason of their large diameter, and 
they not infrequently give trouble from heating. The general name of 
radial valve-gear has been applied to such valve-motions as transmit a 
motion to the valve-stem from an arm, one end of which moves in a 




JOYS VALVE GEAR 



Fig. 625. 



closed curve and which has another point constrained to move in either 
an open or a closed curve by its connection with the frame through 
levers or slides. The closed curve described by the first point is usually 
a circle, an oval, or an ellipse, and motion is imparted from an eccentric 
or a crank or by the connecting-rod. 

The best-known valve-motion of this type is Joy's valve-gear, shown 
in Fig. 625 as applied to a marine engine, and in Fig. 626 in outhne. 
It has been used quite a little in both marine and locomotive service. 



690 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

It will be seen that the motion originates from a point on the connecting- 
rod which gives, from its connection to a secondary link, a reduced 
motion to the lever which drives the valve-stem. The point D describes 
an oval. The other end of the link slides in a curved path to provide for 
the back-and-forth motion of its first end. The reversing effect is 




Fig. 626 

caused by the angle at which the curved slot is inclined. A variation 
in the point of cut-off is produced by the variation in the throw of the 
valve-stem, which is least when the curved slide is midway between 
its forward and backward position. The slide may be replaced by 
causing the point K to vibrate from its connection to a link whose 

HORiZOrfTAL ENGINE WITH JOY'S GEAIf. 




Fig. 627 



radius is the same as that used in describing the slide / in Fig. 625. 
The Joy valve-gear is made up entirely of pin-joints for the moving 
parts, and gives equal lead, cut-off, and port-opening in both gears. 
The objection to it in locomotive practice is the exposed position of the 
links outside of the frames, where accidental injuries are most likely 
to affect them. Fig. 627 shows this gear applied to a stationary engine. 
Other gears in this class are those of Marshall, Brown, Hackworth, 
and Angstrom. 



REVERSING VALVE-GEARS. LINK-MOTIONS 



691 



467. Walschaert Valve-gear. Almost the only other form of valve- 
gear which has contested with Joy's the sole acceptance with locomotive- 
builders is a Swiss motion which bears the above name of its inventor. 
Fig.. 628 shows that the double motion is derived partly from the engine 
cross-head and partly from a crank or eccentric 90° from the main 
engine-crank. The valve gets an aggregate motion from the cross-head 
and from the curved link, and reversing is effected by reversing the 
motion derived from the eccentric-rod when the shding-block is on one 




"'^T'^ Eccentrie 



Ceotral Lino of MotioD 




side or the other of the fixed center of motion of the curved link. It will 
be seen that such a gear produces no variation in the lead. Fig. 629 
shows the American form of this gear as put out by the Baldwin Loco- 
motive Works. 

468. Allen Link-motion. The link-motion first proposed by Allen 
is the one which in a modified form is known as the Pius Fink gear. It 
has no eccentric-rod properly so called, but the link is an integral part 
of the back strap. The half of the strap which carries the link has a 
fulcrum-pin by which it is attached to the engine-frame above or below 
the shaft, so that the motion of the center of the link is an aggregation 
of the back-and-forth motion of the strap as a whole, and the up-and- 
down motions caused by the constraint of the fulcrum-pin which prevents 
undesired motion of the point where it is attached. Fig. 630 shows the 
Allen link. If the engine is not intended to reverse, but variation in 
point of cut-off only is desired, the slot in the upper half above the 
fulcrum-pin only is needed. As the valve-stem approaches the center- 
Hne of the shaft, its motion diminishes. In the Porter- Allen engine the 
separate exhaust-valve is driven from a fixed point near the end of the 
slot, giving constant travel, release, and compression. The eccentric 
of the Allen link is set opposite or at 180° with respect to the crank. 

469. Link-motion for Riding Cut-off Valves. It adds considerably 
to the complication of a valve-gearing which uses an independent cut- 



692 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




REVERSING VALVE-GEARS. LINK MOTIONS 



693 



off valve when it is required to reverse the motion of both valves. The 
cut-off valve may have its independent link-motion coupled to the 
reversing-levers so that one motion reverses both the main and the cut- 
off valve. To avoid this complication many designers have arranged 
the cut-off valve to work with an eccentric 180° distant from the main 
crank, so that the cut-off valve works equally well with forward and 
with backward motion of the main valve. 

Link motions for locomotives operated wdth cut-off valves are 
identified with the names of Polonceau, Gonzenbach, and Meyer. 
The student is referred to special treatises for study of their peculiarities. 

470. Power Reversing-gears. The Stephenson link-motion has been 
a favorite valve-gear for marine engines, for reversing rolling-mill 
engines and similar massive designs. The weights and masses to be 




Fig. G30. 



moved and the necessity for quick action have compelled designers to 
apply mechanical power to reverse the link-motion. Steam power or 
hydraulic pressure have been the usual methods. Steam power has 
been applied first by means of a reversing-engine on whose shaft was a 
screw. The nut of this screw travelhng in one direction or the other 
moved the link into forward or backward gear. The second plan is to 
attach the rod of the tumbUng or rock-shaft to a steam-piston in a 
C5dinder. This would be a too rapid reversing motion, so that it must 
be controlled for speed and the piston must be held still or latched at 



6'94 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

the desired point of the motion of the hnk. This is attained by attach- 
ing to a prolongation of the piston-rod a second piston which moves in a 
cyhnder filled with water or oil at both ends. The motion of this oil- 
piston from one end of the cylinder to the other will be controlled by the 
passage of the oil through a pipe connecting the two ends of the cylinder 
through a valve. The velocity of motion is controlled by the greater 
or less opening of this valve, and when the valve is shut the piston is 
locked in place and the link is held. The third form applies the principle 
of steam steering-engines to the link-motion. The motion of the engine 
to throw the link is continually closing the admission-valve of this 
auxiliary engine, so that continuous motion of the hand is necessary to 
keep the link moving. When the hand stops the engine stops. This 
prevents the attendant from jumping the valve-gear. 

Hydraulic-pressure reverse-gear is available where water under 
sufficient pressure can be had from pumps or accumulator. The power 
cylinder is sufficient with hydraulic pressure, since a closure of both 
inlet and outlet valves to the piston locks it rigidly in place and holds 
the link at the desired position. The piston-rod of the hydraulic 
cylinder either throws the link directly, or operates a tumbling or 
rock-shaft to which the link is connected by rods. 



CHAPTER XXIX. 

VALVE-GEARS FOR VARIABLE CUT-OFF. 

471. Variable Cut-off and Throttling Control. The treatment in 
Chapter XVII concerning expansive working of the steam (paragrafs 
297—299, and 304, 305) should have made it clear that as the work 
varies the area of the indicator card should be made to vary with it, 
so that the speed of the engine shall be kept constant. This might be 
done either by throttling the steam-pipe area by a valve without modi- 
fying the timing of the point of cut-off; or the point of cut-off might be 
varied without affecting the initial pressure of the entering steam. The 
first or throttling system is independent of the design or functioning of 
the valve-gear: the second system works through the valve-gear and 
the design of the latter is conditioned by this fact. The argument of 
paragrafs 299 and 305 showed this automatic control by the governor 
of the degree of expansion to be of advantage when the expense of first 
cost was justifiable. Hence a study of the methods by which the 
governor of the engine can be made to vary the expansion may precede 
a study of the governor mechanism itself. The same methods apply 
also to varying the point of cut-off or degree of expansion by hand or 
through human intervention. It will not be worth while to use an 
automatic governor control of cut-off in engines of propulsion, such as 
the locomotive, the motor-vehicle, or the marine engine; nor in engines 
for pumping or for hoisting where the work does not vary irregularly; 
nor for many uses where the variation is in starting only, and while the 
engine man will be in attendance in any case. The same is true where 
close regulation to speed is not necessary or where fuel economy is not 
significant. 

In general there will be four methods used to attain variable 
cut-off whether by hand or by governor: 

1. To vary the throw of the valve, in the sliding type. 

2. To vary the lap of the valve, in the sliding type. 

3. To vary the angular advance of the valve. 

4. To vary the point of trip or release, in both sHding and lifting 
type. 

472. Cut-off Varies by Varying Throw of the Valve. It will have been 
apparent from the solution of the problem in paragrafs 438, 439, that 

695 



696 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

with the lap fixed by the invariable length of the valve, the shorter the 
throw relatively to this lap, the earlier the cut-off. Hence with all the 
link motions which have a reversing function the cut-off becomes earlier 
as the gear is hooked up, making the throw less. This is done by hand, 
or in such designs as the Allen or Fink link of paragraf 468 it may 
become automatic by causing the governor, as the engine speeds up, 
to lower the valve-stem operated by the slot in the link, so as to 
diminish the throw. The slider in that slot can be raised and lowered 
by hand, if desired, by having it mounted upon a screw. 

The second gT-eat method of securing cut-off by varying throw is to 
arrange the eccentric so that the effective valve-crank can be made less 
or more. In the discussion of shaft-governors hereafter it will be seen 
that it is quite easy to vary the eccentricity of the eccentric without 
changing its angular advance by means of an equilibrium between 
revolving weights and springs (Fig. 651). The eccentric can be made to 
have a variable eccentricity, by mounting it upon the outside of another 
eccentric which shall be adjustable under the outer one. The effective 
eccentricity of the outer one can thus be varied between the sum and 
the differences of the eccentricities of the two eccentrics. These two 
systems fall short of the ideal in that the exhaust functions are modified 
also as the cut-off varies, and release and compression are not constant 
with variable cut-off. 

The third method of varying the throw is to be met in cam valve- 
gears. The profile of the cam can be made to be different at different 
transverse sections. A mechanism which slides the cam underneath 
the roller which it drives will cause the valve to open, farther and 
remain open longer when the valve-stem is driven by the wider and 
more prominent profile of the cam (Fig. 611). This lengthwise sliding 
of the cam on the cam-shaft can be done by hand or by a governor. 

473. Cut-off Varies by Varying Lap of Valve. The discussion of lap 
in Chapter XXV, which showed it to be a matter of construction of the 
valve itself, might appear to indicate that the lap of a given valve is 
not a variable. This is true for a valve-gear dependent upon one valve 
only, or in which the steam-ports and cut-off edges of the valves are 
parallel. The discussion in paragraf 438 will have shown that as the 
lap is increased the cut-off becomes earher. 

Fig. 631 shows the form of riding cut-off valve discussed in paragraf 
440, having the simple expedient of making the valve in two parts, which 
are attached to the valve-rod by being fitted to screws on that rod. It 
will be noticed that one screw is right-handed and the other is left- 
handed. When the rod is turned around its axis by a hand-wheel or 
through similar means outside of the valve-chest, the two blocks are 



VALVE-GEARS FOR VARIABLE CUT-OFF 



697 



Connects to Condenser 



drawn together or separated according as that motion is right-handed 
or left-handed. A swivel-joint in the valve-rod permits this motion of 
adjustment, and an indicator bearing a graduated scale can easily be 
attached to the valve-stem connection, so as to indicate the effective 
length of the valve from out to out, and the point of cut-off which 
belongs to each particular 
length of the valve. This is 
called the Meyer cut-off. 

For adjustment of cut-off 
over a wide range, this com- 
pels a number of turns of the 
screw and stem, and hence is 
an inconvenient thing to effect 
by the governor. To get 
around this, the ports in the 
main valve have been inclined 




HZJ 

Fig. 631. 



to each other on the upper face, and the riding- valve made trapezoidal 
in plan. It will be apparent when the spindle AB in Fig. 632 is 
revolved through a small angle, the effective length of the valve 
between cut-off edges is varied, and the cut-off made early or late. 
The riding- valve can be plane (Fig. 632) or cyhndrical (Fig. 633).- 

A scheme for securing an equivalent for the variation of the lap is 
represented in Fig. 634, in which it will be observed that the steam-edge 
of the port is made with a false seat to which motion can be imparted 
through the rod C. As cut-off takes place with the outer edge of the 
valve as it approaches its central position from its extreme throw, it will 
be apparent that to have the valve-seat moved to meet the valve is to 
produce the same effect as lengthening the lap of the valve over a 
stationary port. It is only necessary that provision should be made to 
vary the angular advance of the eccentric which drives the rod C. This 
shows a balanced valve also (paragraf 447), as well as Fig. 631. 

474. Cut-ofif Varies by Varying Angular Advance of Eccentric. To 
avail of this method to vary the cut-off, the eccentric cannot be positively 
fastened to the shaft. There must be some provision similar to the 
methods described in paragraf 460 to adjust the relation of the eccentric 
to the crank, or the mechanism of the shaft-governor (see Chapter XXX) 
must be so connected to the eccentric as to produce this effect. The 
objection will be that, while cut-off will become earlier with increasing 
angular advance, the exhaust events are distorted. An exception of 
note is to be met in the valve-gearing of the Buckeye engine, in which 
the ingenious expedient has been adopted of mounting the cut-off 
valve mechanism upon a roc king-arm which is a part of the main- valve 



698 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



gear. Increasing degree of expansion without interference with other 
functions follows from simple change of the angular advance. 

475. Cut-off Varies by Varying Point of Release or Trip. This form of 
variable cut-off gear has been fully discussed in Chapter XXVII. The 
primary intent of most trip-gears is to have the period of the release of 
the admission-valve variable at will while keeping release and com- 





FiG. 632. 



Fig. 633. 




Fig. 634. 



pression constant. The cam valve-gears can be similarly made variable 
by so arranging the cam itself or the lever which it operates that an 
adjusting mechanism shall cause it to come out of contact at the desired 
point of the stroke. The methods for accomplishing this result are very- 
numerous and can be quite simple. 



CHAPTER XXX. 

GOVERNING AND GOVERNORS FOR STEAM ENGINES. 

480. The Problem of Governing. In paragraf 403 the distinction was 
made between the function of the fly-wheel and that of the governor in 
the steam engine. The governor is to keep the engine to its mean speed 
under all variations of load; the fly-wheel is to prevent variations from 
the mean speed during a stroke or when the mean effort is adjusted to 
the mean resistance for a given stroke or a small number of them. 

The governor problem appears in two categories: The first is to 
prevent the engine from racing or running away when the load is sud- 
denly taken off; the second is to keep the engine to an assigned speed 
under all variations of load with a definite limit of excess or deficiency. 

A governor which keeps the engine making its revolution in the same 
or equal time under all variations of the load is called an isochronous or 
equal-time governor. The governor which only precludes racing need 
not be isochronous. Perfect isochronism is the ideal; practical iso- 
chronism is realized when the variation from speed is only two per cent. 

While governors are intended to control the energy delivered to the 
cylinder, it is not convenient to make them do this directly. It is easier 
to have the variation of speed made the element or factor which puts 
the governor into action. The less the variation of speed required to 
affect the governor, the more sensitive it is. 

481. Classifications of Governors. Steam-engine governors may be 
variously classed. They may act to throttle the steam in the pipe 
(paragraf 304), or they may act to vary the duration of the admission 
but not its pressure (paragraf 305). The first class will be called 
throttling-governors, the second class cut-off governors. 

Governors are nearly always founded upon an equihbrium or balance 
of forces at the desired or normal speed, so that the disturbance of the 
equihbrium due to a change of speed calls for an adjustment of their 
mechanism, and the motion of the adjustment alters the distribution. 
A direct relation between speed and centrifugal force has long induced 
designers to plan their governors in dependence upon the energy gener- 
ated in revolving weights by centrifugal force. A second classification, 
therefore, would be to divide governors into centrifugal, inertia, and 
resistance governors according as variation in speed is desired to pro- 

699 



700 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

duce a variation in equilibrium between these forces and some other in 
opposition to them. The class of centrifugal governors may be divided 
into two according as the acceleration due to centrifugal force is 
balanced by the force of gravity or the tension of springs. The spring- 
governors are sometimes called balanced governors, because most 
of them will work in any position. The resistance-governor is operated 
by a variation in the resistance offered to motion by some part or organ 
of its construction. This is most usually done by the use of a fluid, 
when the governor becomes a fluid governor; or by a braking action 
which is stronger or weaker than the normal according as the speed 
increases or diminishes. The inertia-governors depend upon the 
principle that the variation in inertia of a revolving mass follows 
instantly upon a tendency to vary the speed; and change in position 
following the change of inertia adjusts the mechanism. 

Governors may be classified again according to the method adopted 
to effect change in the valve-gear or the distribution. Under this group- 
ing they would appear in three classes: The first and most generally 
used might be called position-governors, in which the weights or masses 
produce their effect to diminish or increase the energy admitted to the 
cylinder as the position of these weights is varied by the preponderance 
of weight or some other of the forces which are in equilibrium at normal 
speed. 

The second group would be called disengagement-governors. These 
are of several types, but their underlying principle is that at normal 
speeds the governor is without effect upon the regulating-train or is 
disengaged from it. As the speed varies above and below that of 
normal rate the governor engages or puts in motion a train of mechanism 
whereby the supply of energy is diminished or increased. This is a 
specially useful type of governor for water-wheel motors, but can easily 
be applied to engines. It will be seen, however, that it is likely to be 
a better type for safety against racing than to secure continuous 
isochronism. 

The third group in this class will be called differential governors. In 
this class a certain normal speed is fixed by braking, or a uniform 
resistance or a separate mechanism, and when the governor revolves 
at this speed it is without effect upon the regulating-train. Above that 
speed or below it the difference causes a motion of readjustment to take 
place, and this difference according as it is positive or negative closes or 
opens the supply of energy. 

Governors may be divided again according to the arrangement or 
disposition of their mechanism. This gives rise to the division into 
spindle-governors, which revolve around a vertical axis or spindle, and 



GOVERNING AND GOVERNORS FOR STEAM ENGINES 



701 



shaft-governors, which revolve in a vertical plane with the main shaft of 
the engine as their axis, or around an independent horizontal axis. The 
class of shaft-governors requires no connecting mechanism between 
the engine-shaft and the governor. The spindle-governors are con- 
nected to the engine-shaft by belting or gearing or both. 

483. The Mechanics of the Governor. The conical pendulum was applied as 
a governor by James Watt, and is often called the fly-ball or Watt governor in the 
form in which he used it as a means to prevent racing. Fig. 640 shows three types 






Fig. 640. 





Fig. 641. 



of arrangement, the rise of the plane of the balls as they revolve, lifting the sliding 
collar and closing the valves to which it is connected. In Fig. 641 let: 

w = the weight of the ball. 

h = the height of above A 5 in inches. 

H = the height of above AB in feet. 

r = radius of ball path in feet. 

c = centrifugal force acting horizontally. 

n = number of revolutions of per second. 

N = 60 n = number of revolution of ball per minute. 

V j= linear velocity of balls in feet per second. 



702 



MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



Then, from similar triangles 



H w w gr J rr 9'"' 

- = - = — 7 = ^ and H=^ 

gr 



But since v =2 nrn 



whence 



H 



gr^ _ 0-816 

4 Ti^r^v? 'n? 



35230 



That is, the height h depends only on N , and is independent of the weight of the 
balls, length of arms, or other structural details. If these values for h be computed 
for successive changes in N of 10 revolutions per minute, the following table results, 
from which it appears that the change of height which is depended on to close the 
valve falls off rapidly as the height decreases ; or that regulation is much more prompt 
as the height h is kept large. That is the same as to say that the governor is more 
sensitive as the height h is kept large, or the angle AOB at the vertex is kept small. 
This might have been foreseen, since the centrifugal force varies with the speed, and 
the centripetal force does not. • 



R.p.m. — N 


Height h in Inches. 


Change h' — h' . 


60 


9.79 




70 


7.19 


2.60 


80 


5.51 


1.68 


90 


4.35 


1.16 


100 


3.52 


0.83 


110 


2.91 


0.61 


120 


2.45 


0.46 



To keep the apex angle AOB small, and the height h large, the expedient of an 
extraneous force additional to the action of gravity on the balls has been intro- 
duced to load the governor. That is by a weight on the spindle or by a spring the 
former force w becomes iy'== AC' in the right hand of Fig. 641. Then OB becomes 



OB' = h' and if the extra load on each ball be called 



W 



so that w' 



W 



35230 

iV2 



(^)=^(-?) 



The governor can now be speeded up with advantage and yet keep the same power, 
as the weight of the extra load is not exposed to centrifugal action. If the loading 
weight be applied by a leverage of any sort to give it a mechanical advantage, and it 

35230 / ijrm] 

N' [ ~^ 2 J 



moves y times as fast as the balls do, then h 



i 



GOVERNING AND GOVERNORS FOR STEAM ENGINES 



"03 



In the usual Porter governor (Figs. 500, 654A), the links are made of equal length, 
making y therefore equal to 2 ; so that 

33230,, ^ , 

v' = .-r- (1 + m). 



If the extra loading is done by a spring instead of a weight the simplest case is 
where the spring has no initial tension when the balls are down, and it is compressed 
upon their rise. Then if the link is I feet long, and the height when the spring is 

compressed to balance the centrifugal excess over the weight is H feet, then l — H=~ 

and the compression in the spring compressed y feet may be called Py. Then as 
before 

H _ W + Py W + 2PI -2 PH 
r ~ c ~ 0.00034 Wrr)? ' 
hence 

i/ (0.00034 Wv? + 2P) =W + 2 PI 

In a horizontal governor TT^ disappears from the numerator so that 

2 PI 
0.00034 W7i' + 2P 

for such horizontal spring governor. 

No gravity governor of the simple conical pendulum type can be truly isochronous. 
It can be made sensitive, and so approach isochronism. 
The crossed arm governor, approximating to the 
parabolic arc for the path of the balls is approximately 
isochronous (Fig. 643). The nearer the points of 
pivot of the arms are to the spindle the more stable 
or sluggish the governor. The vertical center of the 
arms is their intersection. 

By eliminating gravity and substituting spring 
action a true isochronism can be secured. If the 
type be chosen which is used in the Parsons- 
Westinghouse turbine (Fig. 473), and shown in 
diagram Fig. 642, let c be the force on each ball 
due to centrifugal effect and p the pressure from the 
spring upon that ball to draw it back. Within a 
restricted range of flexure of the spring p will increase directly as r; so that p can be 
called Kr, where X is a constant dependent on the stiffness of the spring. The 
link radius n is often made equal to r, but may be greater or less. Calling 
ri = ar, then: 




Fig. 642. 



cri = pr and 0.00034 Wr'^an? = Kr^ giving n^ 



K 



0.00034 Wa 



Now the weight W of the balls is constant for any given governor, and a is a 
constant for that design; or for that governor the quantity n? or n is a constant. 
From which the deduction is that there is only one speed at which there is equi- 
librium of spring pressure and centrifugal force. Above that the balls tend to fly 
out; within it, they tend to come in by the spring. Any speed change from the 
normal sends the valve open wide or tight shut, and tends to make the engine keep 
to the desired speed. In other words the governor is always at work except at the 
normal speed. This is the reason for the vogue of the shaft governor. 



704 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

483. Defects of Governors. The mass or weight required to overcome 
the resistances of the valve or gear which the governor adjusts, or which 
give power to the governor, is the occasion for an inertia effect. This 
slows down the response of the governor to change of speed, and makes 
it sluggish. The same mass or weight causes friction at the joints or 
rubbing surfaces; lack of effective lubrication also tends to sluggishness. 
Lack of power to operate its valves and gear is also a defect. Hyper- 
sensitiveness in governors intended to be astatic, or give isochronism in 
the engine, keeps the governor chasing over its range of position, so 
that it is never at the point of control at mean speed desired, but is 
'* hunting " the engine, and always out of its place. This is corrected 
by dash-pots, which will be seen on many of the illustrated engines. To 
reduce the defects of sluggishness and inertia, the following designs are 
in use. 

484. The Loaded Governor. Porter's Governor. The discussion 
of paragraf 482 showed that an extra weight on the axis of the governor 
spindle, which was not exposed to the centrifugal effect, enabled the 
governor to have a higher rotative speed and sensitiveness, but without 
the injury of an inertia effect, or adding to friction. Figs. 644 and 654A 
show loaded governors. The pear-form of the weight is characteristic 
of the Porter design. 

485. The Parabolic Governor. The parabola has the property that 
its subnormal is constant and equal to the parameter. If the balls be 
made to travel outward upon an arc of a true parabola, the height h in 
the treatment of paragraf 482 is this constant subnormal: hence at any 
speed, the balls will be indifferently at the extreme outward position, 
tending by their position to shut steam off completely; or they will be 
all the way in, opening the steam admission wide, and this without any 
change in the value of n or N. Such a governor will readjust the 
steam distribution with startling rapidity, but it is hypersensitive, or 
too sensitive to be of practical use. The effect of sudden changes of 
load with such a governor would be to introduce momentary departures 
from the normal or mean speed. This difficulty of the exact parabolic 
governor is corrected in two ways. First, by attaching a dash-pot to 
the governor-spindle, and secondly, by the use of approximate parabolas 
for the path of the balls. The dash-pot method attaches to the adjust- 
ing spindle a piston which fits in a small cylinder filled with oil. The 
resistance offered by the oil to displacement from one end of the little 
cylinder to the other through and around the piston serves as a brake, 
to prevent jumping or racing or hunting, while no real resistance is 
offered to changes of position. The approximate parabolic governor is 
sometimes called the cross-armed governor. The suspending links are 



GOVERNING AND GOVERNORS FOR STEAM ENGINES 



705 



hung from points which are the centers of a circle whose radius is the 
radius of curvature of the parabola for that part of its arc over which the 
ball is to travel {BC in Fig. 643). This type, first introduced by 




Fig. 643. 



Farcot in France, has been widely used. Greater power can be given 
to such a governor by loading it. Fig. 644 shows the Steinlen loaded 
approximate parabolic governor. 

486. Balanced Governor without Spring. Many ro^ms of governor 
have been devised to secure an approach to isochronism by aiming at 
balancing the effect of gravity in part and 
thus make the governor more acutely sensi- 
tive to changes of speed. The direction in 
which this has been sought most frequently 
is to connect a second smaller weight to 
the suspending link on the opposite side 
of the vertical spindle. This arrangement 
has taken many forms, but perhaps that 
shown in Fig. 645, which shows the Buss 
governor, presents a European type as well 
known to Americans as any other of its 
class. The Babcock & Wilcox governor, 
shown in Fig. 646, will stand as representa- 
tive of another solution, in which the weight 
of the balls is eliminated from the forces in 
action by the connection through the 
radius-rods P to the revolving spindle. 
Since the lengths of the rods n and P can be so related to each other 
that P shall be one-half the length of n, a parallel motion will be formed 




Fig. 644. 



706 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

so that the balls fly in and out, not in arcs of circles as in previous 
spindle designs, but in a horizontal plane. They do not have to be 
lifted, therefore, in order to travel in a larger circle, and an increased 
speed is not needed to maintain them in their advanced position. That 
there may be a force to bring them in, the spindle is lifted by the weight 
W operating through a bent lever. The proportions of this lever and 





Fig. 645. 



Fig. 646. 



the variation of its arms are so adjusted that the centrifugal force at 
any given speed will just balance the weight in all its positions. Any 
increase in speed will cause the balls to preponderate, and a diminution 
of speed will cause the weight to preponderate. By connecting the 
spindle to the cut-off mechanism, the cut-off will be changed until the 
speed comes again to the standard, where the force resident in the weight 
balances the downward pressure on the spindle due to the centrifugal 



GOVERNING AND GOVERNORS FOR STEAM ENGINES 



707 



force of the balls. By increasing the weight W or diminishing it the 
desired speed can be varied. The dash-pot serves to prevent instability 
or jumping. 

487. Balanced or Spring Governors. A much nearer approach to 
isochronism is made by those forms of governor which substitute a spring 
for the force of gravity to draw in the balls and open the valve when 
the speed falls. This has been a very fruitful field for governor designs, 





Fig. 647. 



Fig. 648. 



and successful spindle-governors and all shaft-governors depend on this 
principle. They approach isochronism more closely because the tension 
of the spring can be made to increase as the centrifugal acceleration 
increases, so that the revolving weight and the spring are in equilibrium 
only at the normal speed. 

Early forms of successful spring-governors of the spindle type are 
Pickering's, Fig. 647, and Waters's, Fig. 648, Gardner's and Wright's, 
Fig. 649. In Pickering's governors the jointed link of the typical 
fly-ball spindle-governor is replaced by a flat steel blade to which the 
balls are secured rigidly through their centre of gravity. There are 
usually three balls, and the curve of the springs is such that in action 
they take the curve known as the cyma-reversa. In the Waters governor 
the balls are similarly mounted on flat-blade springs which are bent 
before fixing to the spindle into the form shown. The object in both 
cases is to get a balance between centrifugal force and the resilience of 



708 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 





Fig. 649. 




Fig. 650. 



GOVERNING AND GOVERNORS FOR STEAM ENGINES 



709 



the spring at the normal speed only, and a preponderance of one effect 
over the other at all other speeds. In these designs the balls are small 
and light and revolve at high speed; and the carrying of the balls upon 
the springs eliminates friction at pin-joints. 

The first spring governor using an initial tension of the springs was 
patented by Chas. T. Porter in 1861. His claim was for the idea of 




Fig. 65]. 



giving to the spring of a centrifugal governor an initial deflection of such 
amount that in every position of the balls the radius of the circle 
described by them and the distance through which the spring is deflected 
shall bear a nearly constant ratio to each other (see paragraf 482). 

488. Shaft-governors. When the vertical-spindle idea is abandoned 
and the revolving mass is attached to the horizontal shaft of the engine 
so that it turns in a vertical plane, the balanced and spring principle is 
a necessity, and gravity must be eliminated. The methods pursued in 
the design of shaft-governors differ very widely, while yet possessing 
much in common. Two pivoted masses- or weights are disposed sym- 
metrically on the two sides of the shaft, and their tendency to fly out- 
wards is resisted by springs either in simple spiral form or in flat-leaf 
form. The outward motion of the weights closes the admission- valve 



710 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

earlier, and the inward preponderance of the springs closes it later. 
Equilibrium exists only at a certain fixed speed, and that speed can be 
varied by varying the spring tension. In Fig. 650 the radial travel of 
the weights rotates the loose eccentric and alters the angular advance. 
It is perhaps more usual to swing the eccentric across the shaft so as to 
diminish its effective eccentricity and the throw and travel of the valve 
as the weights go out. This is the method of the governor in Fig. 651. 
Fig. 653A in the appendix shows a shaft-governor of this type in its 
position of early cut-off on the right and latest cut-off on the left. 

489. Inertia-governors. Fig. 651 will serve as a type of the governors 
which are planned to produce their controlling effect by the change of 
position which will occur when a weighted lever B, pivoted at P, finds 
that the fly-wheel which carries it is lagging behind or overrunning the 
normal speed. At the normal speed a weighted lever occupies a certain 
position between the stops shown in the cut in equihbrium with the 
spring tension, which at rest would hold it against one of them. When 
the load varies the speed of the fly-wheel, the revolving weights keep on 
at their previous speed, thus changing the relation between the lever 
and the fly-wheel, and adjusting the admission mechanism until the 
normal speed is regained. This can also be done by mounting the 
weighted arm nearer the circumference of the fly-wheel, or, balancing 
the drag or lag of the weight due to inertia by a proper spring. 

The instability of inertia-governors, which is the consequence of their 
sensitiveness, makes it necessary that many of the forms should be 
steadied from too rapid fluctuation by dash-pots (E in Fig. 652). 

490. Spindle and Shaft-governors Compared. The shaft-governor 
must be a cut-off governor. The spindle-governor may be either a 
throttling or a cut-off governor. The shaft-governor turns at the 
speed of the engine, and is valuable only at high rotative speeds. The 
spindle-governor can turn faster than the engine if desired, and can 
work at low rotative speeds. In some recent designs the shaft-governor 
has been geared from the main shaft so as to be run at a different speed. 
The shaft-governor is compact, and is directly connected to the engine- 
shaft, and therefore prompt in action. The spindle-governor is con- 
nected either by belt or shaft to the main shaft, and a breakage of such 
belt or the accident of its slipping or running off its pulley permits the 
engine uncontrolled to run away. The balls drop as the governor ceases 
to turn, and the valves open wide, letting full power on the engine. 

491. Resistance-governors. The class of resistance-governors is less 
in use under high-speed conditions than it was when rotative speeds 
were low. A very successful form of such governor was one in which 
the opening of the throttle-valve was controlled by a rod attached to a 



GOVERNING AND GOVERNORS FOR STEAM ENGINES 



711 



weighted piston in a little cylinder. A small pump operated by the 
engine-shaft forced oil or water under this piston, while a graduated 
orifice permitted it to flow back into the suction of the pump. When 
the engine speeded up, the oil or the water was pumped into the cylinder 
faster than it could flow out, so that the piston was lifted and the energy 




Fig. 652. 



reduced. When the pump and engine workea too slowly the weighted 
piston descended and more energy was admitted to the cyhnder. 

Another form of resistance-governors has a propeller-wheel revolving 
in oil within the cylindrical casing. The revolution of the inclined 
blades tends to force the propeller shaft lengthwise, and this tendency 
is resisted by weight or spring. When the engine speeds up above the 
normal, the spring is compressed and the weight lifted; and conversely, - 
as the speed falls the weight or spring slides the shaft. Another form 
replaces the propeller by a paddle-wheel which turns in oil within a 
ribbed casing. The paddle-wheel tends to carry the oil around with it, 
and the oil catching on the ribs tends to revolve the casing. This ten- 



712 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

dency is resisted by a weight acting upon an increasing leverage, so 
that equilibrium can only exist at a definite speed. In these two 
latter forms the position of the spindle and of the casing as determined 
by the speed adjusts the admission of energy to the cylinder. (Fig. 655.) 
Resistance-governors are isochronous in principle, but lack sensitive- 
ness to respond instantly to minor variations of speed. The objection 
to them is that they absorb continuously a certain amount of power, 
while in the balanced types, when no rearrangement of forces occurs, 
nothing but friction has to be overcome. Resistance-governors will 





Fig. 655. 



become large in proportion as the density of the fluid decreases. This 
has stood in the way of attempts to make fan-governors which would 
revolve in the air. The superior viscosity of oil makes is a better resist- 
ance than water. 

493. Electromagnetic Governors. Governing devices of this sori; 
have been applied with success in central-station work, both with steam 
and water as a source of motor energy, where the resistance is the gener- 
ation of electric current by dynamos. In this case the speed and power 
of the engine are controlled directly by the resistance by simple devices. 
A governor of such sort consists of an electromagnet or solenoid to which 
current is supplied from the line wire. When the electromotive force 
rises beyond the normal, a motion of the armature towards the magnet 
takes place against the force of the weight or spring. The latter is so 
adjusted as to hold the armature in a fixed position at a normal speed 
and intensity of current. It is only necessary to connect the armature 
to the valve-gearing by convenient means. When the spring is in 
excess there is too little current, and more energy should be admitted. 
When the magnet is in excess there is too much current, and the energy 
of the engine should be cut down. Governors of this sort will vibrate 



GOVERNING AND GOVERNORS FOR STEAM ENGINES 713 

on each side of the mean intensity of the current and keep up a perpetual 
approach to isochronism. 

493. Dynamometric Governors. Designers of governor apphances 
for their engines have sought to make the resistance control the effort 
in the cylinder directly, and without having to make use of variation of 
speed indirectly to control the effort. While the electromagnetic 
governors just discussed (paragraf 492) belong to this class in one sense, 
they are indirect methods except where the work of the engine is the 
generation of electric energy. The best known attempt to solve this 
problem directly was to make the belt -wheel a sort of transmission- 
dynamometer. The belt-wheel was not keyed to the shaft, but was 
driven by the latter through a second wheel whose arms were connected 
to the arms of the belt-wheel by means of springs. It is obvious that 
with a given resistance in pounds on the belt-wheel the two sets of arms 
would separate until the stress in the springs balanced the resistance. 
From that time on the two wheels w^ould remain in the same relative 
position until there was a change in the resistance, to which the springs 
would instantly respond and produce a new relation of position. The 
change in the angle between the driving arm on the shaft and the driven 
arm of the belt-wheel was made to vary the admission, so that the 
energy of the cylinder varied directly as the load. Such a governor was 
properly called a "weigh the load " governor. The difficulty connected 
with it and with the other governors by which the same object has been 
sought has been that the adjustment of the valves could not be con- 
trolled within sufficiently narrow limits. Even with dash-pots to 
deaden the oscillation it has not been convenient to secure isochronism 
of the engine. It was hypersensitive, and adjusted the valve-gear 
through a wider range than actual variation in the load required. 

494. Safety-stops. It will have been noticed from the preceding that 
in the case of fly-ball governors the fall or drop of balls in gravity types 
and the drawing in of the balls in spring types are the motions by which 
the valves are opened wide. This fall or drop of balls will happen in 
belted governors when the belt runs off and breaks. As soon as the 
engine is released from the control of the governor, and the latter from 
its position admits the maximum energy to the cylinder, the engine runs 
away, with probable disaster in its train. To diminish this danger 
many forms of governors have attachments which are called safety- 
stops. Their object is to close the valve controlled by the governor 
when the latter shall have lost its normal action by some breakage so 
that the balls fall. They are of two kinds, mechanical and electrical. 
In the mechanical safety-stops the usual underlying principle is to have 
a detent or trip which the governor in its normal position does not touch, 



714 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

but which will be released should the drop of the balls permit the descent 
of a rod or lever to its lowest point. Such drop of the balls will release 
the detent, which shall permit the action of a spring or weight powerful 
enough to close the valve when thus released. In many constructions 
the setting of the weight or spring and its catching by the detent will be 
done by hand after the engine has reached its normal speed and the 
rotation of the balls has lifted the tripping-rod out of the way. In 
another form the spring is set by a ratchet motion, so that it sets itself 
after the normal speed is reached. To protect the engine from the 
danger of racing when a governor belt breaks, a tightener pulley which 
rests on the belt in normal working can be so connected to a throttling 
lever or quick moving valve (paragraf 241), that the fall of the tightener 
pulley and the arm which carries it will close the throttle if the belt 
parts, allowing the tightener to drop. 

The electrical safety-stops usually act in essentially the same way, 
but the convenience for the transmission of power which is offered by 
electric methods permits their functions to be extended. A very 
practical form of electrical safety-stop has a weight or spring powerful 
enough when released to force the balls to the top of their range, and 
close off admission to the cylinder. This weight or spring is held out of 
action by a detent attached to the armature of an electromagnet. The 
armature may be held away from the magnet with a spring of graduated 
force, so that the normal current in the coil shall not be able to draw 
the armature to the magnet and thus release the weight. Overspeed, 
exciting the magnet beyond the equilibrium-point, w^ill release the detent, 
releasing the weight and throwing the governor-balls up. This same 
result can be attained by differential currents. A convenient and use- 
ful extension of this idea has been to connect the releasing detent by 
buttons or switches to different rooms or departments. In case of 
accident in such department, by pressing the button or throwing the 
switch, the weight controlling the governor-ball would be at once released 
and the driving-engine would be stopped (Fig. 656). 

Automatism with instantaneous action is a prime requisite of such 
devices, and it is very desirable that they should not have to depend 
upon the setting or memory of the engine-runner to be made ready. 

495. Marine-engine Governors. The locomotive and the traction 
engine commonly use no governor. Their resistance does not vary 
suddenly, and a human intelligence must always be at hand to control 
them in any case. In marine engines, however, while in smooth waters 
the same condition prevails, in rough weather the pitching of the vessel 
may release the screw from its resisting medium and suddenly take the 
load off the engine. Obviously this is a source of danger both to the 



GOVERNING AND GOVERNORS FOR STEAM ENGINES 715 

long and flexible shaft and to the screw itself when it suddenly re-enters 
the water while moving at too great velocity. Many marine engineers 
prefer to meet this difficulty by keeping one of their staff continually 
at the throttle-valve in bad weather, and no form of revolving governor 




exactly meets the case. Some of the shaft-governors operating by 
springs independently of gravity would meet the case most nearly 
but for the size of the engines in question and the increased compli- 
cations and weight which would be introduced. A form of marine 
governor which has been introduced in many marine engines is a species 
of pendulum arrangement operating a valve in the steam-pipe. Fig. 657 



716 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

shows a general detail of such a device. When the vessel is on an even 
keel, the pendulum attached to a spherical casing hangs vertically, and 
all steam-openings coincide so as to leave free passage from boiler to 
engine. As the ship pitches it changes the angle of the steam-pipe, to 
which a fixed casing is attached, while the pendulum-ball remains 
vertical. The effect of this pitch or send of the ship slides the openings 




Fig. 657. 



over each other, and throttles the passage for steam to the engine. If 
the pitch is enough to send the openings past each other, no steam 
can get through. The pendulum swings steam-tight by means of 
flexible or spherical joints at the opening through which it protrudes. 
Most engineers even with such a governor attached to their engines do 
not relax their vigilance at the throttle. 

496. Connections of the Governor to Control the Engine. The student 
is referred to the discussion in Chapter XXIX for the methods which 
may be used to make the governor in any of its forms control the speed 
and energy of the engine. The number of combinations possible is very 
great, since almost any kind of governor can be applied to produce 
variation in the point of cut-off by the methods discussed in Chapter 
XXIX. The methods for hand-adjustment of such variation are usually 
made automatic by properly gearing the governor mechanism to the 
mechanism which operates the valves. 



PART VI. 
CHAPTER XXXI. 

ENGINE AUXILIARIES. _ THE CONDENSER AND ATTACHMENTS. 

500. Introductory. In the discussion of Power Plant Auxiliaries in 
Chapter XIII a somewhat arbitrary division was made into the 
auxiliaries primarily related to the boiler or pressure generator plant, and 
those attaching to the engine-room or pressure converting plant. The 
feed-pumps and feed-heaters for examples may be called engine-room 
auxiliaries with almost equal logic to that used in allotting them to 
the boiler-plant. In the condensing engine particularly the pumps are 
rather elements of the condensing apparatus, and may be treated under 
this head. The condenser is, however, so manifestly an engine attach- 
ment that with its attachments it falls into the class now to be con- 
sidered. 

In paragrafs 299, 306, and 307 of Chapter XVII the argument for 
selecting the condensing principle for securing low terminal and back 
pressure in expansive working was very completely reviewed, provided 
this was economically defensible. What is now to be done is to examine 
the apparatus required to realize the condensation desired. Reference 
should be specially made to objections 3, 4, 5, and 6 of paragraf 307. 

501. The Principles of the Steam Condenser. The principles under- 
lying the condenser or vacuum chamber of the condensing steam-engine, 
whether turbine or reciprocating, are derived from the properties of 
steam. If the steam exhausts into the atmosphere or into any vessel 
open to the atmosphere, the pressure therein cannot fall below 14.7 
pounds absolute, which is the pressure above a zero of pressure belonging 
to one atmosphere, or at the pressure at which the air stands by reason 
of gravity, or the weight of air surrounding the earth. If the steam is to 
be reduced in pressure below this at exhaust, it must be done by leading 
it into a closed chamber, and tight enough to prevent leakage of atmo- 
spheric air into it from the atmospheric pressure without. Secondly, 
the steam must be cooled below 212° F. or 100° C. if its pressure is to 
be less than 14.7 pounds absolute, or one atmosphere, within this cham- 
ber. This cooling can be done by any means which shall be continuous. 
The vacuum chamber must be kept cool, so that its metal does not get 
hot from the incoming heat of the steam. Hence both the steam and 
the air-tight vessel must be cooled. With what? The two cooling 

717 



718 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

media which are cheapest to buy and to apply are water and air. Water 
will be used where possible, because it has a greater cooling effect per 
pound than anything available known. Its specific heat is unity; or it 
takes less weight of water to cool a given weight of steam, and smaller 
pumps to handle it than any other cooling medium. Air is used where 
water is hard to get or carry or is costly for any reason; but it is much 
less effective, requires to be kept moving by a fan or rapid motion, and 
the surface for equal cooling effect has to be much larger. Water is 
therefore the standard. 

When the steam meets the cool surface of metal or water and drops 
down temperature, a third effect is produced. The volume hitherto 
occupied by steam is now filled with water, resulting from the conden- 
sation due to the temperature drop; with some water vapor of the 
lower tension due to the lower temperature; and with leakage air, coming 
in with the steam, or with the cooling water, or through cracks or 
porosity of the metal. The change to water is responsible for much of 
the lowered tension, but some water has heat enough to boil at the 
lowered pressure and the vacuum is not theoretically perfect. The air 
is not effected by the temperature drop: to eUminate all watery vapor 
so great an excess of cooling water would be required that it is not 
economically practicable. 

In the fourth place, the condenser or vacuum chamber, supposed 
air-tight, will begin to fill with the water resulting from the condensation 
of the incoming exhaust steam. As soon as it fills completely, the 
vacuum disappears and is lost, and if there is no relief valve, the exhaust 
steam keeps coming in and backing up pressure until it balances the 
boiler pressure, and the engine stops. Hence this water from conden- 
sation must be gotten out of the condenser, and the air which also 
came in. If this is removed by a pump, it will be called an air-pump. 
The cooling water for lowering temperature and therefore pressure will 
be called the ''injection" water. The supply of injection water will 
come from a " cold-well." The delivery of water warmed by the 
cooling of the steam will be to a " hot-well." The hot water coming 
from the condensed steam will be returned to the boiler, and this will be 
done by the feed pump. 

502. The Vacuum Gage. The pressure in the condenser being less 
than 14.7 pounds, or one atmosphere, cannot be registered by a common 
steam gage, whose zero point or reading is at the pressure of such one 
atmosphere. But a gage is easily made on exactly the same principle, 
except that it is designed to record the pressure outside of its spring 
(paragraf 171) or its tube, so that the needle reading will be the differ- 
ence between the atmospheric pressure outside and the pressure within- 



THE CONDENSER AND ATTACHMENTS 719 

such tube. Such gage reads zero as it Hes exposed to the air both 
outside and inside. When connected to a vacuum chamber it reads 
negatively as it were, or registers the pressure below the atmosphere in 
the vacuum chamber. To get total pressure then, the steam gage 
reading above zero or atmosphere is added to the vacuum gage reading 
below that same zero. The vacuum gage in pounds reads to 15; it 
sometimes is graduated to read inches of mercury, or up to 30 or 31. 

503. The Weight of Injection- water. The injection- water must come into 
the system in sufficient mass per unit of time or per pound of steam to be condensed 
to condense first the steam to water by absorbing the latent heat of vaporization ; and 
secondly to cool that hot condensed water to its own final temperature. Experience 
shows that to try and get a lower final temperature than 110° — 130° F. with an 
average of 120° costs more than is gained in smaller plants, without elaborate equip- 
ment. Hence if 

H = total heat units in one pound of steam at the temperature of the steam as it 
enters the condenser from the cylinder. This is the total heat at that pressure 
in steam tables. 
h = the heat per pound of the hot condensed water leaving the condenser. This is 
the temperature of that water, when the unit is one pound. 
Then one pound of entering steam must dispose of a quantity of heat in heat 
units = H — h. 
If now 

Q = the weight of injection required: 

t = the temperature at which it enters the condenser. 

T = — the temperature at which it leaves the condenser. 

Then if the metal of the condenser keeps at a constant temperature the equality must 
exist that 

Q{T -t) = liH -h); 
or 

^ T -t 

If the temperature of the air pump discharge as hot water be called V, then h = V. 
The prevailing practice in design is to call H the total heat of steam at 30 pounds 
pressure, or 1190. This makes 

_ 1190 - V 
^ ~ T-t ' 

If the injection be put at 60° and the discharge at 110, this will make Q = 21.6 
times the weight of steam in the minimum case. To allow for warmer injections, 
it is usually called 30 to 35 with jet condensers and 60 to 75 with surface types. 

504. The Volume of the Air Pump. The air pump, which handles both the 

injection- water and the condensed water, requires to dispose of Q -f- 1 pounds per 

pound of steam condensed. If the water at the usual temperatures of the con- 

1728 
denser be taken as weighing 61.7 pounds to the cubic foot, then = 28 inches 

61.7 

will be the volume occupied by a pound. The pump volume per minute will there- 
fore be for weight of steam W, 

F =(Q + 1) x|5 xTf . 



720 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



But the actual volume to be displaced must be greater than this by an allowance 
for the inefficiency of the pump, and for the fact that it must handle air besides the 
water, and the quantity of air is not always predictable. The actual displacement 
will therefore become 



F = (Q + 1) 



(!?)-• 



For the air-pump for the surface condenser, see paragraf 510. The results of 

28 
experience make — E == 1 for horizontal double-acting air-pumps and equal to 0.75 

for vertical single-acting pumps. 



%\ 



E^ 



"W 



^ 



r^ 



A 



505. The Jet Condenser. The simplest type of condenser brings the 
injection-water directly into contact with the steam to be condensed 
and the resultant water to be cooled. The most effective method 
of bringing them together is to divide the injection into a series 
of fine streams entering in jets; hence such condensers are called 
jet condensers. Fig. 660 shows the direct or jet condenser as used in 
river-boat practice where the injection comes from the water outside 

of the hull. It will be seen 
that the steam escaping from 
the cylinder enters the con- 
denser at the side and near 
the top below a partition 
which runs across the con- 
denser. This partition is per- 
forated with a great number 
of holes about one-half inch 
in diameter. The pipe enter- 
ing the side of the condenser 
and working upward through 
the perforated partition is the 
injection-pipe, which comes 
from a suitable opening in 
the hull through the skin of 
the vessel. The injection-pipe 
has a valve in it, operated by a lever or by a hand- wheel (see Fig. 389), 
whereby the flow of injection-water can be cut off and controlled. It 
will be apparent that if there is a vacuum in the condenser, and the 
opening of the injection-pipe is below the surface of the water outside 
of the hull, atmospheric pressure mil force the injection into the con- 
denser with considerable energy, so that the injection-valve is usually 
only partly open. In such river-boat engines as are presented in Fig. 389 
there are usually three entrances to the injection-pipe. The usual one 
used will be the bottom inlet, opening through the hull near the keel 



lirn 



Fig. 660. 




THE CONDENSER AND ATTACHMENTS 



721 



and of course always under water. The second one will be the side 
inlet, which will be used only when such shallow water is to be feared 
that there would be danger that the bottom inlet would draw in mud 
or become stopped with solid matter. 
The third inlet will be from the 
bilge of the boat, and will be called 
the bilge-injection. It will be used 
only when from a leak or an accident 
an excess of water has come within 
the skin of the vessel, so that the 
propelling engine can be used to empty 
the bilges and lighten the duty of 
the bilge-pumps proper. It will be 
seen that the injection descends 
across the exhaust-steam in a finely 
divided shower, whereby the least 
weight of water need be used. Some- 
times the injection is sprayed into 
the steam through a simple nozzle 
like the rose-nozzle of a flower 
watering-pot (Fig. 668). The open- 
ings through the hull are protected 
on the outside by gratings or strainers, 
and in the inside are valves close 
to the skin which are called " sea- 
cocks " (Fig. 663). If the injection- 
pipe is broken inside the hull and 
there are no sea-cocks nor any means 
of closing them from the decks the 
engine-room becomes flooded with 
water from without. 

The more modern and usual form 
of the jet condenser for land practice 
abandons the idea of the larger 
volume of the condenser — perhaps 
one-half or two-fifths of the cylinder 
volume — and utilizes the advan- 
tages of rapid flow of the injection-water to entrain with it the disen- 
gaged air. Hence the cross-section is much less, and is made pear- 
shaped in form with the smaller area at the bottom to compel the more 
rapid flow of water and stop any tendency of air-bubbles to ascend 
and break the vacuum. In Fig. 661 the steam comes in at A and 




Fig. 661. 



722 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

meets the injection water entering at B. The latter is sprayed by the 
inverted cone at D and intimate mixture is effected. The hand-wheel 
at E controls the thickness of the water film for best effect. The pump 
at G keeps up the vacuum by continuously exhausting the water from 
the space F. This type is more hable to quick flooding with water than 
the previous type of larger volume and cross-section if the pump fails 




Fig. 662. 



to operate from any cause. The injection backs up into A and over 
into the engine, where it makes trouble unless a relief valve is supplied. 
(Fig. 675.) The combined injection and condensed steam water pass out 
at J to the hot well. The left-hand portion of Fig. 663 shows such a 
condenser on a fresh-water vessel, with the injection entering at E 
through the sea-cock, and past the controlling valve D to the con- 
denser AT^; thence outward and overboard through T. The pump L acts 
as a feed pump taking such water as is required from the pipe G under 
this set of conditions. The suction or exhausting pump may be also a 
volute or centrifugal pump, either turbine or motor or engine driven 
(Fig. 662). 



THE CONDENSER AND ATTACHMENTS 



723 



I 




.yl'i;' 



724 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

506. The Surface Condenser. In the other type of condenser, the 
injection does not meet the exhaust steam for direct contact and 
mixture, but the two are kept in separate circuits. The steam meets a 
coohng metallic surface of sufficient extent, usually of tubes of brass 
or copper coated usually with tin on both sides to prevent corrosion and 
lessen galvanic action. These tubes are one half or three quarters 
of an inch in diameter. Fig. 664 shows the usual arrangement of such 
a surface condenser in the older marine designs, which use sea-water 
for cooling, and in Fig. 662 at the right hand is the more modern 
cylindrical type, with the course of the circulating cooling water made 
obvious. The pump F will be now a circulating pump, to take in the 
water from the sea-cock and overcome the resistances of the tubes 





Fig. 664. 



and lift the water the few feet necessary to send it overboard again 
through the valve V. In Fig. 664 the air pump is vertical and single- 
acting at the side of the condenser. In Fig. 663 it is horizontal and 
double-acting, drawing out the condensed water into the receiver K 
and pumping it from L, which is the air pump, back to the boiler. The 
air which separates in K is drawn off by the suction of the pump F. 
There is often no cogent reason other than convenience determining the 
question whether the injection-water should circulate within the 
battery of pipes while the steam is on the outside, or whether this plan 
should be reversed. English naval practice adopts the latter. It is 
most usual in the merchant marine to have the steam on the outside, 
because less difficulty is met from the clogging of the condensing sur- 
faces by the condensation of the lubricating material on the cool sur- 
faces of the condenser, and it is easier to clean the outside of the tubes 
than the inside, and the tubes can be drawn through the tube-plate 
more easily for cleansing. The scale from sea-water used in circulation 
is removable without taking out the tube; tubes can stand internal 
pressure better than external; the water circulates better; a large surface 



THE CONDENSER AND ATTACHMENTS 



725 



meets the steam; the design is simple and compact; and a packing can 
be used which contains organic matter. For the Enghsh plan it may 
be said that most of the lubricant is caught at the first tube-plate; the 
flat surfaces of the condenser have only upon them the light pressure 
of the water in circulation, and not the larger pressure of the atmosphere 
against the absence of pressure within; the metal of the condenser 
radiates less heat in the engine-room. On the other hand, packing of 




.SSSSV^SSSSS'.SSV-sS^S^^^^SS^S<^sv^.-...<^^vvv..^^<v.V^V..SV^^VSV,^-VVVV^ 



Pig. 665. 



the tube-joints must be done by some device which will not be affected 
by the steam. The steam enters the surface condenser usually at the 
top, and the cold injection-water enters it at the bottom and as it 
becomes warm in cooling the tubes it is forced upwards so as to meet 
the hottest steam when it is itself warmest. This plan of having the 
injection travel against the steam secures the greatest difference of 
temperatures in all parts of the condenser as a whole, and transfer of 
heat is most rapid with greatest difference of temperature between the 
body to be cooled and the absorbent material. The condensed steam 
gathers in the bottom. Fig. 665 shows a form of a surface condenser 
designed to avoid one or two main difficulties of surface condensers. 
By reason of the conditions to which they are exposed the tubes are 
subject to changes of temperature which cause them to expand and 
contract, and makes it difficult to keep the tubes tight where they 
enter the two heads shown in the previous sketch. This has been 
sought in the prevalent designs by making an expanded or fixed joint 



726 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

at one end, and at the other fixing a species of stuffing-box kept tight 
with compressible packing and permitting the tube to sHde. 

Fig. 666A in the Appendix presents a grouping of such methods of 
flexible joints. 

A is Howden's wick or hemp joint. 

B and C are Lighthall's, packed with papier-mache, 

D is Winton's hard-rubber ring. 

E is Spencer's rubber washers. 

F is Marshall's moulded rubber joint. 

G is Stimer's tube. 

H is Hall's stuffing-box. 

/ is Chapman's joint with Babbitt-metal calking. 

J is a rubber washer with lock-nut. 

K is Sewell's joint, compressing rubber by a cover-plate gland. 

L is Archbold's, with brazed brass wire to prevent creeping. 

M is Wilson's, similar to K except that each tube is packed separately. 

N is Horatio Allen's soft wood packing. 

Q is Todd's method. 

The joints from A to 7 do not permit the removal of the tube without 
having to be themselves renewed. The cover-plate plan K packs all 
tubes at once. 

The Wheeler condenser, shown in Fig. 665 and in detail at P in 
Fig. 666A, secures the tube tight in one end only by screwing, and the 
circulating water, instead of passing through the tube completely, is 
made to flow through the closed tubes by means of the smaller inner 
tube which is not attached directly to the outer. The difficulty from 
the tube-joints was a very serious obstacle to their first introduction 
on sea-going vessels. Their use now is universal, since this difficulty 
has been overcome. 

The accepted rule for computing the number of square feet of tube surface in the 
surface condenser is that of Jay M. Whitham from experiments by Shock and others. 
In this: 

S = square feet of condensing surface. 

W = weight of steam to be condensed per hour. 

L = latent heat of steam at the condenser temperature, from steam tables. 

T = temperature of the condenser, taken the same as that of the water discharged 

from air-pump. 
t = average temperature of injection or circulating water, taken as the half sum of 

its initial and final temperatures. 

Then: S = W X jg^^^. 

In average conditions -^ = 17, 



THE CONDENSER AND ATTACHMENTS 



727 



so that there will be required one square foot heating surface to 10.6 to 11 pounds 
of steam delivered per hour; or three square feet per average horsepower; or four 
square feet per kilowatt. 

In the tropics, where the circulating water is hotter than in cooler climates, more 
surface will be required. In special conditions where the cooling water is unlimited 
as in surfaces of coils under the hull of a boat used as a condenser, 50 pounds of water 
will be condensed per square foot per hour. In mine or water- works pumps, where 
the discharge can go through the condenser without perceptible increase in tem- 
perature, 20 to 40 pounds per hour per square foot can be counted on. When reduced 
to gallons, about one gallon per minute per horsepower is a value much used for 
the amount of circulating water. It is more usual to provide for excess of circulating 
water over the lower quantity computed in paragraf 503 for the jet condenser, and 
this explains the larger figure of 60 to 70 pounds of cooling water per pound of steam 
condensed. 

507. Jet and Surface Condensers Compared. In the jet condenser, 
the injection and condensed steam water are mixed; the air-pump must 
handle both, plus the air from leakage and entrainment. Hence the 




Fig. 667. 



injection must be good enough to use in the boilers, and only a part of 
the mixture of injection and condensation is required for the boiler- 
feed. The rest must be wasted, or the method of feeding used which 
is discussed in paragraf 146. 

The surface condenser, while more heavy and bulky to handle and 
cool a given weight of steam discharged as exhaust, can be used with 
any water of reasonable quality. The condensed steam leaves the sur- 



728 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



face condenser as distilled water with no impurities in it except the 
lubricating oil, and is therefore a most excellent material to pump back 
into the boiler if the oil can be extracted from it. The surface con- 
denser has for this reason occupied the field with vessels traversing salt 
water, and has furthermore a wide scope on land in places where the 
available water contains solid matter or salts or acids which would be 
injurious to boilers. The same water is used over and over again, and 
the only addition of bad water which has to be made to that which 
filled the boilers in the first place is that which is lost by leakage at 
safety-valves, whistles, and joints. The steam-circuit is practically a 
closed one. The surface condenser for sea-vessels adds from ten to 
eighteen per cent to the first cost of the engines, but is more economical 
of fuel for them than jet condensers would be. In Fig. 667 is a type in 
which the exhaust enters at the bottom and the injection at the top. 
The circulation passes three times through the length of the cylinder. 

508. The Cold-well Cooling Towers. In stationary practice on land 
the water for condensation and the injection must be supplied from a 
reservoir. In cities having a water-supply the city water can be used 

for this purpose, but ordinarily the 
quantity needed for a plant of con- 
siderable size will compel the engineer 
to consider other means. In the 
older designs it was very common to 
immerse the condenser in the tank 
from which the injection was to be 
drawn (Fig. 668) ; and even where city 
suppHes under pressure are to be had, 
it is preferred not to connect the 
condenser to the mains, but to take 
the injection from a tank in which 
the supply of pressure-water shall be 
controlled by float-valves or ball- 
cocks. The expense of city water 
has compelled many proprietors to 
sink artesian or other private wells 
for the purpose of controlling the 
necessary quantity of injection- 
water, but even this is expensive and not always practicable. The 
tank from which the injection is taken was called by the early 
designers the cold-well, and latterly considerable pains have been taken 
to make it possible to use the same injection-water over and over 
again without making the cold-well of unmanageable size. 




Fig. 668. 



THE CONDENSER AND ATTACHMENTS 



'29 




SUCTION TANK. 



Fig. 669. 



730 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

Two general methods have been followed in the solutions which have 
been sought for this problem. The first has been to construct a series 
of shallow troughs in which the warm injection-water flowed in the open 
air exposed to the action of the natural winds. These troughs were 
arranged one over the other with a slight grade, so that the water flowed 




zigzag fashion from the top to the bottom, and after leaving the lower 
end of the latter flowed back to the well. The prolonged exposure in 
thin films to the vaporizing action of the open air and the coohng caused 
by such vaporization resulted in a considerable lowering of the tem- 
perature of the injection. The other plan, of modern introduction, is 



!l 



THE CONDENSER AND ATTACHMENTS 731 

to cause the injection to descend in a closed tower in a fine state of 
division over tile or cypress wood or wire gauze arranged corn-cob or 
grating fashion with maximum surface and interstices between. A 
current of air forced by a fan causes a vaporization of the film of warm 
water pouring over the exposed surfaces, and the air-cooling and 
vaporization combined withdraws the heat from the injection, so that 
as it falls into the cold-well at the bottom of the tower it is in condition 
to be used again. This appliance has been in successful operation for 
some years, and is warranted wherever the cost of condensing water 
per annum without such device w^ould exceed the interest upon the cost 
of the plant and the expense connected with operating it. Fig. 669 
illustrates this arrangement using a fan and jet condenser and tile 
surfaces: Fig. 670 shows the tower at work in natural draft of air as a 
chimney without fan, and some fuller details of the complete installation. 
The condenser is here of a type to be later discussed (paragraf 513). 

509. The Air-pump and Foot-valve. The vacuum created by con- 
densing the steam by the injection must be maintained in the condenser. 
The condensed steam and injection would rapidly fill the volume of the 
condenser if no means were taken to empty it. Furthermore, all 
natural water and the steam contain a certain quantity of air which 
undergoes no condensation or reduction of volume, and whose presence 
in the condenser would soon destroy the vacuum created by condensa- 
tion. Some means must therefore be provided to draw from the con- 
denser the condensed steam, the injection, and the air. While the 
pump handles water mainly, the handling of the air is its most exacting 
requirement, and in starting, it pumps air. Hence it gets its name. 

From Figs. 664 and 668 it will appear that single-acting vertical 
pumps have been used for this purpose; and from Figs. 661 and 669 
that double-acting horizontal pumps can be used. The occasion for 
these chfferences will be discussed in paragraf 511. 

The air-pump must meet the difficult condition of withdrawing water 
and air from a vessel within which the pressure is less than the atmos- 
sphere, and therefore atmospheric pressure cannot be counted on to 
fill its barrel as is the case with the ordinary lifting-pump. If the piston 
in the air-pump in Fig. 668 be supposed to be rising in its barrel, and the 
bottom of that barrel opens into the condenser through the valve which 
separates them, it will be apparent that as long as the pressure in the 
air-pump is greater than the pressure prevailing in the condenser the 
valve cannot open. The rise of the air-pump piston must create below 
it a rarefaction or vacuum greater than that in the condenser before the 
valve will open and any equalization of pressure occur. Furthermore, 
the water in the bottom of the condenser will only flow through the 



732 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

foot-valve of the pump by gravity, unless there is enough of it to seal 
the connection between the two volumes, and will then only rise in 
the air-pump sufficiently to counterbalance the differences in pressure. 
The bottom of the air-pump and the foot-valve must therefore be below 
the bottom of the condenser, so that the water may fall out of the con- 
denser by gravity. When the air-pump reverses and begins to descend, 
the foot-valve closes and remains closed during the descent of the 
bucket. As the bucket goes farther down it strikes the water which 
has flowed from the condenser, and therefore the bucket-valve opens 
by excess of pressure below, and the bucket descends through the water 
to the bottom of its stroke. In its ascent the water above the bucket 
closes the valves and seals the piston while the cycle of the first stroke 
is repeated. 

The foot-valve in most American marine vertical single-acting air- 
pumps direct-driven from their engines is a flat rubber flap of the 
necessary thickness (inch to inch and a half) which seats upon a grated 
inclined partition. Access to this valve for renewal and repair is had 
through a bonnet or cap formed in the casting just over the grating. 
The air-pump bucket-valves are also usually circular rubber disks, 
which are prevented from rising too far by brass guards. They also 
seat upon grated openings, and are easily accessible from .the top of 
the air-pump. From the top of the air-pump the combined injection 
and condensed steam are discharged to the organ of the condensing 
engine which is called the hot-well (Fig. 668). 

With the surface condenser the air-pump is still required, but its 
function is slightly different. As the injection does not meet the con- 
densed steam, the air-pump does not have to handle the former, but 
has only to draw out the condensed steam and the air which gets into 
the condenser with the steam and by leakage. This latter however is 
a much more important factor in percentage of material handled in the 
surface-condenser system than in the other. Hence a very common 
practice is to make the factor (R^^) in paragraf 504 to be five times 
as large as for the combined system for a vertical single-acting pump, 
and 9 times for the double-acting pump. That is, the air pump dis- 
placement in cubic inches per minute is D = 5TF and D = 9TF for these 
two cases. 

510. The Wet and Dry Air-Pump. Advanced designing has pre- 
sented many examples of separating the two functions of the air-pump 
and using a separate pump for each. One will be connected to the 
bottom or lower part of the condenser to handle the water, while at a 
point above the level which water will ever reach will be a second pump 
working on relatively dry air, or a mixture of uncondensed vapor and 



THE CONDENSER AND ATTACHMENTS 



733 



air. This dry-air pump principle enables each pump to be of smaller 
volume than if one cyhnder had both functions to perform, and also 
secures a better vacuum, since the dry-air pump is more effective, both 
by location and functions, for the removal of air than the single wet 
punip can be. This system will be found in all modern stationary 
power plants which operate with condensation. The opening at the 
top of Fig. 667 will be for such dry-air pumps. These will often be 
of most careful design, with minimum clearances and mechanically 
operated pump-valves. With them a vacuum within a half a pound of 
the absolute limit of pressure for that day has been attained. 

Fig. 671 shows a form of combined wet and dry -air pump known as 
the Edwardes design where the usual foot-valve is dispensed with and 
the water flows by gravity to the bottom of the air-pump through 




Fig. 671. 



ports in its barrel. The top of the barrel is closed so that on the descent 
of the piston the pressure is much reduced above it by the enforced 
expansion of what air it contains. The bottom of the piston is conical, 
and as it enters the water in the bottom of the pump, the liquid is 
forcibly and positively displaced through the ports landing on top of 
the piston, at the same time that the air above the water rushes as 
shown by the arrow. The piston rising closes the ports communicating 
to the condenser, and the increase of volume below it causes water and 
air to flow out together into the pump as before. Any excess of water 
to be provided for while the ports are covered passes out by displace- 
ment through the valve at the right. 



734 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

511. The Independent Air-pump. The beam-engine of most types 
drives its own air-pump. The inverted vertical reciprocating-engine 
for marine practice has also driven a special beam or lever from its 
cross-head to operate its air-pump (Fig. 664). See also Figs. 384 and 
402. 

Many advantages follow from abandoning the principle of the 
attached pump (paragraf 147) and driving such air-pump independ- 
ently of the main engine, either by a steam cylinder, an electric motor, 
or by a transmission from the shafting which the main engine drives. 
In turbine plants the air-pump must be independent. 

The principle offers these advantages: 

1. The pump can be located anywhere. The attached principle 
compels the air-pump to work in the plane of the main engine if directly 
attached, and this may make the location for the air-pump either 
cramped or inaccessible or inconvenient. 

2. The air-pump being independent of the main engine can be run 
without it. This is of advantage in starting the main engine, since the 
vacuum in the condenser can be created before steam is turned on to 
the main engine. 

3. The air-pump can be run at varying speeds while the main engine 
is run at a constant speed. This enables the designer and .runner to 
provide for varying temperatures of the injection-water according to 
the season of the year, and in marine practice according to the latitude 
and corresponding temperature of the ocean-water. The air-pump can 
further be run faster than the normal rate in case of leakage into the 
condenser which it may not be convenient to arrest. The vacuum 
will be maintained as it cannot be with the attached pump. 

4. Since the air-pump can be run faster, and can usually be double- 
acting, it will be much smaller than the attached pump. This is a 
saving in bulk, a saving in weight, a saving in friction, from the lessened 
weight, and the small-diameter cylinder has a less clearance-volume, 
which is always troublesome when air is to be rarefied. 

5. "By detaching the air-pump, which is a water-pump as well, the 
speed of the main engine is not limited by the limitations of satisfactory 
working of the air-pump. The high rotative-speed engine can thus be 
conveniently condensing. 

The only objection to be urged against the independent air-pump is 
that the small steam-cylinder which drives it uses steam less econo- 
mically than the large cylinder of the main engine. This is not true 
when the air-pump is motor-driven. The necessary clearance- volume, 
although smaller in the independent engine, is filled and emptied more 
often. 



THE CONDENSER AND ATTACHMENTS 



735 



The superior convenience of the independent principle has made it 
a feature of much recent designing, particularly for high speeds and of 
necessity for turbines. It will be seen from Figs. 665 and 672 that it 
is very simple to combine the air-pump and the circulating-pump for 
surface-condenser practice so that one steam-cylinder shall drive both 
pumps. This makes an arrangement which is both convenient and 
very economical of space. The inertia effect of the levers, piston, and 
water of the attached system are not negligible at even moderate speeds 
(paragraf 260) and must be computed in a complete treatment. This 
plan is practically limited to slow and massive engines. 

512. The Circulating Pump. If the surface condensing system is 
used, the injection-water of the jet system becomes the circulating 




Fig. 672. 



water through the tubes. Fig. 663 shows the general requirement of 
overcoming a few feet of head and the resistance to motion through the 
tubes from friction, bends, and valves, friction of the condensing tubes, 
and to lift the water through the few inches of difference of level between 
the water outside and the discharge-level of the overboard-valve. B}' 
reason of the small resistance and the large volume of water which are 
the conditions of such circulation (seventy times the volume of feed- 
water required by the engine), centrifugal pumps have been the very 
prevalent type of circulating-pumps. They are driven by their own 



736 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

independent engines or by motors. More recent American practice 
introduces reciprocating-pumps for this kind of work with satisfaction 
(see Figs. 665 and 672). When single-acting reciprocating-pumps are 
used, the volume of the cylinder is from one twentieth to one thirtieth 



Adjustable Relief 
Valve 




H 



Fig. 673. 



of the steam-cylinder volume. For small launches where the quantity 
of steam to be condensed makes such an arrangement practical, a form 
of surface condenser has been used which consists of a coil of pipe 
zigzagging on the outside of the hull on both sides of the keel. The 
steam passes through the inside of this coil of pipes, and the motion of 



J 



THE CONDENSER AND ATTACHMENTJ 



737 



the boat causes a continual impact of cool water against the coil and 
produces the same phenomena as by the circulating-pump. It has been 
found, as might be expected, that the more rapid the motion of the 
vessel through the water the more efficient are such condensing coils 
(paragraf 506). The extra resistance offered by such coils is the 
compensation for the avoiding of the circulating-pump, but in small 
boats it is a distinct gain to get the bulky condenser outside of the hull. 

513. The Barometric, Injector, Siphon, or Gravity Condenser, The 
wet-air pump is to draw out water of condensation from the bot- 
tom of the condenser (paragraf 510) and the dry-air pump to exhaust 
the air and watery vapor uncondensed. If the condenser can be put 
over 32 feet up in the air, with an air-tight pipe descending from it and 
water-sealed at its foot in the hot-well (Fig. 670), it is plain that atmos- 
pheric pressure on the water in the well will balance a column in that 
air-tight pipe only 32 feet upward, and that above that level will be 
practically a Torricellian vacuum if the 
air can be gotten rid of. The later and 
better system is to use a dry-air or 
vacuum pump as shown in Fig. 670; 
the other plan is to entrain the air in the 
rapid flow of the water of injection in 
carefully moulded nozzles ^ (Fig. 673). 
The Torricellian principle, with the 
vacuum pump, makes the condenser a 
barometric tube; the jet or siphon in 
action gives the name of siphon to the 
type; in both the withdrawal of excess 
water above the 32-foot limit is by 
gravity and not by any pump. 

Instead of the air-pump, however, the 
injection-water has to be lifted to the 
height of the condenser; but power is 
not required all the way. Atmospheric 
pressure is behind the pump suction, 
and it need only lift through the differ- 
ence in height and overcome resistances. 

The early forms were an elevated pot (Ransom's) but they did not 
adequately get rid of the entrained and leakage air. 

Fig. 674 shows detail of the head of the barometric type, with the 
vacuum chamber on top, and special by-pass injection to condense 
vapor therein. The spraying cone is constructed to secure fine division 
of the jet, and is held in place by an adjustable spring which thins the 




Fig. 674. 



738 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




Fig. 675. 



THE CONDENSER AND ATTACHMENTS 739 

jet as the injection pressure diminishes. The water used is thus made 
altogether effective. It is desirable both in the barometric and the 
siphon types to provide a relief valve and connection, so that from a 
backing up of tho water or other cause the pressure in the exhaust-pipe 
can not exceed the determined limit, and that water from the con- 
denser can not work back into the exhaust-pipe at pressures so nearly 
atmospheric as to give trouble. Fig. 675 shows a float-valve in an 
appendage to the condenser, so arranged that if the condenser floods, 
the rise of the float in the water will open the valve and break the 
vacuum. The engine must thereon operate non-condensing through 
a similar relief valve as in Fig. 670. The spray-cone in Fig. 661 acts 
similarly, since when submerged by water, the water surface alone is 
inadequate. 

514. The Exhaust-steam Ejector Condenser. It early suggested 
itself to apply the principle of induced currents as used in the steam- 
injector to draw up the injection-water and to make use of the living 
force of the water thus set in motion to oppose the 
balancing effect of the pressure of the air. The first 
design of this sort is identified with the name of Morton 
(Fig. 676) in England, and the more usual forms with 
the name of Schutte in Germany and America (Fig. a] 
677). The philosophy of the Schutte injector con- 
denser depends on such an enlargement of the dis- 
charging end of the condenser that when the condensed 
steam and injection leave the outlet they have such a 
velocity as just to overbalance the tendency of the water 
in the hot-well to flow through that outlet back into 
the space where the vacuum due to condensation is 
maintained. As will appear from the sectional cut (Fig. 
677), the steam enters through the side into an annular ^ig 676 
chamber and passes through a series of inclined orifices 
or nozzles. The steam moves with considerable velocity, and draws 
in water from a cold- well A (Fig. 679), and when the steam and water 
meet, the steam is condensed and flows with the rapidly moving water 
out through the discharge into the hot-well B. The discharge is 
sealed as shown in the general view, and the velocity of flow over- 
balances atmospheric pressure on the well. The small steam-connection 
enables water to be drawn into the condenser on the injector prin- 
ciple, in order to start it when water does not flow naturally to this 
level. The by-pass controlled by the valve permits the exhaust to be 
carried to the open air when for any reason it is desirable to run the 
engine non-condensing. 




740 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



6CCTIONAL CUT 

A 



It will be observed that this arrangement also, like that in paragraf 
505, enables the condenser to be operated without the 34 feet of eleva- 
tion. The series of gravity siphon and ejector condensers are all jet or 
direct-contact condensers. 

To start the condenser the starting-jet connected to the small inlet 
marked " Steam" in Fig. 677 is opened and the auxiliary water-valve 
D. When the vacuum has been created, and the main engine is started, 

steam and water meet in the combining- 
chamber and after condensation flow 
together obliquely downward through 
the multiple outlets, creating and 
maintaining a vacuum behind them. 
If the condition of a transverse film of 
water be considered at the orifice of the 
discharge-pipe, it has on its outer face 
the pressure of the atmosphere trans- 
mitted from the surface of the hot-well. 
On its inner face is the pressure due to 
the impact of the moving mass of injec- 
tion and condensed steam discharging 
from the nozzles behind in the injector- 
tube. So long as this latter is greater 
than the former, atmospheric pressure 
cannot exert its effort to force the water 
in the well back into the condenser. 

515. The Hot-welL The dehvery of 
warmed water from the air-pump in 
the jet-type of condensers will be into 
some reservoir, from which the feed- 
pump can take what is desired for 
supplying the boiler. In engines with 
surface condensers the hot-well be- 
comes a much less significant organ, 
because only the condensed steam is delivered by the air-pump 
while the injection or cooling water is passing upon another circuit. 

Referring to Figs. 389 and 359A as a typical river-boat engine with 
attached air-pump, it will be observed that the top of the air-pump, 
which is the discharging end, is enlarged into a cylinder of nearly twice 
the diameter, fitted with a loose cover and a valve. This enlargement 
of the air-pump is the hot-well. In" engines operating with independent 
air-pumps the hot-well will be any convenient tank or reservoir. It 
need not be tightly closed, as there is no pressure in it, and it simply 




THE CONDENSER AND ATTACHMENTS 



741 



has to take care of warm water and serve as a cistern from which the 
boiler feed-pumps may draw their suction. In land practice it is usually 
arranged with an overflow whereby the excess of water not needed by 




Fig. 679. 



the boilers may escape to waste. In river-boat practice the excess is 
usually taken care of by pumps. 

516. The Feed-pump. The feed-pump of a condensing engine draws 
its suction from the hot-well. It may be attached as in the older forms 
(paragraf 147), or independent as in the newer. In the attached system 
it is usual in river-boat engines to attach to the rod of the air-pump one 
or more brackets or half cross-heads, whereby the rod from the beam 
shall operate the pump or pumps which take care of the water dis- 
charged into the hot-well. In Fig. 359A this smaller pump is operated 
from the small beam which drives the air-pump. In engines of this 
class these pumps must have capacity sufficient to empty the hot-well 
continuously. Where the hot-well can overflow as on land, such pump 
need have only a capacity sufficient to feed the boilers with the water 
which they require. In the former case, where the pumps are handling 
an excess of water, it is common to arrange the discharge from the 
pumps to branch into two outlets. One of these outlets goes to the 
boiler, and the other goes overboard through the hull. The valve in 
the overboard branch will control the proportion which goes through 
each branch, since if that valve be wide open the entire deUvery of the 



742 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 




If 



THE CONDENSER AND ATTACHMENTS 743 

pumps must go overboard, because the pressure in the boilers must be 
overcome before the water will flow through the branch connected to 
them. On the other hand, if the valve is shut in the overboard branch, 
the .entire discharge of the pumps goes into the boilers. At intermediate 
degrees of closure, part will go overboard and part into the boilers. 
In the independent systems any form of power driven pump may 
be used. (See paragraf 147.) 

517. Condensers for Steam Turbines. The condensers for a turbine 
plant may be either surface or jet. The surface is probably more usual 
as giving a higher feed-water temperature with a given vacuum when 
the dry-air pump system is used. The turbine is particularly sus- 
ceptible to the advantages of low terminal pressures and temperatures, 
and the better the vacuum the greater the economy. Fig. 680 shows 
a typical auxiliary equipment for a turbine with surface condenser 
with centrifugal circulating pump and reciprocating dry vacuum pump. 

Fig. 481 may also be studied in detail with advantage. All con- 
denser auxiliaries in the turbine plant must be independent, with the 
possible exception of turbo or centrifugal pumps, which may be driven 
by belting from the rotor shaft if they can be conveniently alined. 
Independence of location is usually worth the sUght loss from driving 
these auxiliaries" by electric motor. 

518. Sundry Special Condensers. The pumping engine may have 
a surface condenser installed in its suction or water delivery pipe, using 
its own pumped water as circulation water (Fig. 675 A in Appendix). 
Mine pumps may also discharge their exhaust directly into the water 
they are pumping. 

In motor vehicles, the motion of the car through the air may be used 
to cool the pipes of a surface condenser with the steam within them. 
Here it is usual to supply a fan in addition to secure rapid air circulation 
and the exterior surface of the pipes is increased by metallic fins or 
supplementary areas. 

519. Concluding Comment. The power to drive the independent 
auxiliaries (Fig. 3) should be charged to the main engine to equalize 
the alternative condition where the main engine drives them. Such 
consumption of power is the offset to the theoretical advantage of the 
lowered back-pressure from condensing. 



CHAPTER XXXII. 

ENGINE AUXILIARIES. LUBRICATORS AND LUBRICATION. 

525. Objects of Lubrication. The process of lubrication is to intro- 
duce between two surfaces which have a relative motion of one upon 
another some suitable material to prevent a metallic contact. This 
medium should be one which will further have a tendency to reduce the 
coefficient of friction which would prevail if there were no film of lubri- 
cant present. 

The object or purpose of lubrication is therefore two-fold. The first 
is to keep these contact surfaces from wearing each other; the second 
is to reduce the resistance to motion, or to the transmisson of effort 
from power to resistance. The better the lubrication, the less the 
difference between indicated horsepower in the cylinder and effective 
horsepower at the shaft (paragraf 3). 

526. Lubricants, or Lubricating Materials. The materials. to use for 
lubrication require to be such as have a low coefficient of friction in 
themselves, and which shall be capable of introduction in their films 
between the rubbing surfaces, and shall also not be too inchned to 
leave these surfaces by pressure, by the rubbing or scraping action of 
the surfaces, and by heat. These requirements seem best met by the 
oils, the greases and by graphite. The greases and graphite once 
introduced are difficult to displace by pressure and rubbing; the oils 
are most easily and copiously fed to the desired point 

An oil must not be prone to oxidize or gum by heat and exposure to 
the air; it must not be easily inflammable by heat. It must be free 
from acid as a residual of its refining process. It must not be so viscous 
as to have a high coefficient of internal friction of its own; it must not 
be so limpid or thin as to be squeezed out easily from its contact area. 

The greases should be capable of being gotten into the desired bearing 
surface by pressure, or fusible enough to flow there if melted by a 
gentle heat originating from a friction rise of temperature in the bearing. 
Graphite in fine flake form and free from grit can be introduced either 
as an addition to grease or to an oil. It must not be allowed to seg- 
regate or settle in the oil which carries it as a vehicle. Greases are 
specially convenient in moving elements where an oil would be easily 
thrown out, as in the connecting-rods of locomotives. 

744 



I 



LUBRICATORS AND LUBRICATION 745 

There will be two sets of conditions to be met in lubricating an 
engine, and hence two types of lubricant. The one is the lubrication 
of the cylinder and its valves, which are under pressure and the heat 
of the steam. The condition is particularly exacting when the steam 
is superheated, free from moisture and at high temperature. The 
other set is met in the turning and sliding surfaces of shaft, connecting- 
rod and guides. 

527, Tests of Lubricants. The subject of the various lubricants is 
too broad a one to receive full treatment under present conditions, 
but brief reference may be made to three important tests. An oil is 
liable to fail of its purpose when for any reason it is prone to oxidize 
from heat or use and to become gummy as the result of that chemical 
change. Gumminess is a relative quality, and consequently the test 
to determine this is a relative test between the most limpid and the most 
readily oxidizable of the oils. The test for the gumming quahty of 
the oil is to drop a certain weight or volume of the oil to be tested 
in the middle groove of three, made upon a surface of cast iron which 
is inclined to the horizon at a slight angle.* In one of the other 
grooves is dropped an equal weight or volume of sperm oil, which has 
no tendency to gum, and in the third an equal weight or volume of 
linseed-oil, whose gumming qualities are so great that it is used as a 
drying oil. The three oils slowly run down the grooves, undergoing 
oxidation and becoming more and more sluggish as they flow. The 
distance covered by the oil to be tested, as compared wHh the distance 
covered by an oil having the greatest and least quahty of gumming 
as represented in the other two, measures its excellence in this 
respect. 

The test for acid in an oil is made by putting a small quantity of the 
oil in a test-tube with a little copper scale of the suboxide of copper, 
CU2O. If there are fatty acids present, after some hours' exposure 
and with gentle heat the reactions with the copper turn the solution 
green. If the oil has a vegetable acid, it will turn blue. Further 
qualities of oils for lubricating purposes are determined by their low 
fire-point. If they give off an inflammable vapor by heat, thev are 
of course a dangerous element. 

The third test is for its friction coefficient. This is made in labora- 
tories by a lubricant testing-machine, where the oil is expose'^ to de- 
termined load in a test-bearing, and the resistance necessarv to k^eo the 
bearing from turning with the shaft measures the friction existing in 
the film of oil which keep them apart. 

* One foot elevation in six of length if the oil is to be tested in ordinary air. If 
the slab is heated, the slope may be steeper, and the test will require less time. 



746 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



The mineral oils withstand heat better than most of the animal oils 
and than nearly all the vegetable oils. 

538. Lubrication of Cylinder and Valves. The lubricant required 
within the valve-chest and cylinder must be introduced against the 
pressure prevailing therein. This can be done in one of several ways. 




l|i 



i 



(1) In condensing engines a simple open cup, closed at the bottom 
with a valve or cock, can be screwed into the clearance of the cylinder, 
and opened when the pressure in the cylinder is less than atmospheric. 
This is particularly applicable to vertical cyUnders, but will not 
lubricate the valve. 

(2) The oil can be forced into a cyhnder by a pump either operated 
by hand or driven by the engine, or in large engines by a small steam- 



LUBRICATORS AND LUBRICATION 



747 



cylinder. If driven continuously by the engine or by an independent 
oil-pump, the feeding of oil is continuous and economical (Fig. 685). 
If driven by hand, the supply is intermittent. In compound engines 
this is often used as supplementary to other methods. 

(3) A popular method of lubrication which prevails most widely for 
simple engines is the deUvery of oil by drops continuously into the 
steam-pipe, using a column of water as a source of power. The oil is 
contained in a closed cup from which two connections enter the steam- 
pipe (Fig. 686). Upon the short one, K, close to the cup, steam-pressure 
in the pipe is acting, while upon the other, F, connected to the steam- 
pipe at some distance above the cup, both the same steam-pressure and 





Fig. 686. 



the weight of a column of water condensed in that longer connection 
are acting. This column of water displaces the oil at a controlled rate 
into the surfaces to be lubricated. Its action is continuous. 

(4) What is called the oil-cup or cylinder-cup is a brass vessel with 
a pipe-connection from its bottom, in which is a valve. The cup has 
a lid at the top which is screwed on and steam-tight. When the valve 
in the bottom is closed the oil-cup is cut off from the cylinder and the 
lid can be lifted off and the cup filled. When the lid is in place the 
lower valve can be opened, and the pressure, equalizing, will permit the 
lubricating material to descend into the cyHnder either slowly or fast 
according as the valve-opening may permit. This ^is the air-lock prin- 
ciple, but the feeding by it is intermittent. 



748 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

539. Graphite as a Lubricant. The objection to oiling cylinders with 
fluid oils in condensing engines is the difficulty from the oil in the 
exhaust and in the boiler (paragraf 197). Graphite possesses a lubri- 




FiG. 687. 



eating quality, has a low coefficient of friction, a body which prevents 
it from being forced out of the surfaces where it should act, and further- 
more seems to ffil the pores of the surfaces so that they acquire a 
singularly smooth and mirror-like surface where it has been used. It is 



LUBRICATORS AND LUBRICATION 



749 



introduced either as a powder or in combination with some other 
lubricating material as a vehicle. 

530. Lubrication of Bearings. The bearings in a steam-engine which 
require to be lubricated are those of the shaft, eccentric-straps, the 




Fig. 688. 




Fig. 689. 



crank-pin, and the cross-head pin and guides. The main-shaft bearings 
are the only ones which are stationary so as to be reached by the ordinary 
hand methods, and the convenient and automatic lubrication of all 



750 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

bearings has brought the appUcation of many devices to maintain a 
continuous and abundant supply of oil. What are called sight-feed 
oil-cups are those in which a supply of oil is held in the cup and is 
allowed to drip from its bottom through a valve which controls the 
opening in such a way that the size and number of drops can be seen 
and regulated (Fig. 687). The oil from such cups falls through pipes 
which conduct it to the fixed bearings, where they are distributed by 
proper grooves cut in the bearing by which the motion of the shaft 
makes the oil spread where required. The connecting-rod bearings are 
the most difficult to provide for, because it is a secondary piece sup- 
ported upon two other moving pieces. The crank-pin is lubricated 
either by centrifugal force as shown in Fig. 688, whereby oil received 
near the center of motion is carried outward through a pipe to the 
center of the pin, and is there distributed through a radial hole out- 
wards upon the bearing-surface, or else a flat piece of metal is brought 
against a webbing by the oscillation of the connecting-rod, and wipes 
the excess of oil off the webbing so that it is delivered downwards upon 
the pin (Fig. 689). For the cross-head pin a similar fixed cup is placed 
over the path of the cross-head, having on its under side a piece of 
webbing or similar textile material upon which the oil drops and is 
spread. Illustrations of these methods of lubricating will be seen in 
the various types of engines hitherto presented. 

In large engines with many cylinders and multiple mechanisms a 
practice has been followed of bringing all oil-cups to a few points and 
connecting these oil-cups by pipes to the various bearing-surfaces to 
be lubricated. In vertical engines of the marine type it is usual to 
lubricate the crank-pin by means of a pipe running along the connect- 
ing-rod, and ending near the cross-head pin in a flaring mouth, into 
which the sight-feed oil-cup shall deliver its oil and from which the 
pipe shall carry it to the pin. It will be apparent that, as the cross- 
head travels in a straight line, the mouthpiece will always be under the 
end of the oil-cup in all positions. Bearings have also been made 
self-lubricating by means of rings or chains (Fig. 549) which turn in a 
bath of oil below the bearing, and rest upon the shaft to which they are 
internally tangent. As these rings revolve with the shaft, the oil which 
adheres to them is continuously brought up from the reservoir and 
delivered at the top of the shaft from which it is distributed. 

The certainty of mechanical or forced lubrication for crank-pins, 
cross-head pins and main bearings has given wide acceptance to the 
plan of making these elements with a central and radial holes, through 
which a power pump from the engine, or independently driven, forces 
the oil where required. The principle of splash lubrication of crank 



LUBRICATORS AND LUBRICATION 



751 



cases is also illustrated in many types chosen for presentation of detail 
(see Figs. 345). Cylinders are also oiled by positive pumps. 

Siphons of lamp-wick have also been used as a means of securing a 
continuous slow feed from an oil-cup. The oil rises by capillary action 
in the wick, and when it has reached the bend in the tube within the 
cup in which the wick is placed it descends by gravity down the longer 
arm and is delivered in drops in the bearing below (see Fig. 527). 

Greases are another form of lubricant whose delivery from a reservoir 
can be secured by the slight rise of temperature which will fuse the 




Fig. 690. 



grease; or grease cups can be used in which a more resistant viscid 
grease is forced through the delivery-opening by the pressure of a 
spring controlled by a screw and nut (Fig. 690) . This is particularly 
convenient for lubrication of locomotive-rods, where it is desirable that 
the oil-cup should be closed from grit and dirt, and where the methods 
of the stationary plant cannot be applied. Or, the grease-cup cap or 
piston can be screwed down by hand at intervals; or the descent of the 
displacing piston can be made positive by a mechanical action such as 
shown in the central cut of Fig. 690. Here the revolving crank-pin 
turns the little eccentric and by a ratchet and screw the grease is forced 
down. 

It does no harm for bearings to be run at about 100° to 110° F., or 
so as to be pleasantly warm to the touch of the back of the human 



752 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 



hand. Turbines require no cylinder lubrication, but careful supply of 
oil to the bearings. Here also it is usually forced by a pump. 

It is an economy to catch used oil which has been through the engine 
and use it over again. Care must be taken however to free it from any 
dirt or grit or wearings from surfaces which it may have picked up; and 
after a while, oil loses its capacity to lubricate and must then be thrown 
away. Oils may be filtered for cleansing and successive use. 



PAET VII. 
CHAPTER XXXIII. 

CARE AND MANAGEMENT. ACCIDENTS. 

535. Starting an Engine. So many and so widely different are the 
types of engine and the work which they are to do that anything hke 
detailed instructions is impossible. The best that can be done is to 
lay down certain general principles applicable either widely or univer- 
sally, and leave the application of them in detail to the judgment and 
skill of the operator in each case. 

The most general case would be of an engine for a power house or 
similar plant, and the first distinction which will make a difference in 
procedure must be based on whether the engine is non-condensing or 
condensing. 

536. To Start a Non-condensing Engine. The engine having been 
properly erected and all connections supplied (Chapter XXI), the 
fly-wheel should be turned in such a position that the valves uncover 
the ports, and that there is a turning leverage for the pressure of steam 
to turn the crank. This will be done either by the notches in the fly- 
wheel rim, or by a block and fall, or jack, or other power. 

It is of the greatest advantage in starting to be able to work the 
valves by hand. This is possible in all gears having gab-hooks or their 
equivalent (paragraf 461) and is a feature of all link motions. For the 
first step in starting is to warm up the cylinder by admission of a little 
steam — not enough to turn the cold engine over, but enough to create 
a circulation in the cylinder and out of the open drip connections. 
With the drip valves all open and the steam-pipe previously drained 
of water through its own drips and separator (paragraf 243) hot steam 
is admitted through the throttle- valve by a very slight opening whereby 
it will be allowed to blow through and heat the piston and the walls of 
the cylinder to a temperature sufficient to prevent excessive conden- 
sation. This also rids the steam-pipe of the water which has accumu- 
lated within it. In positively connected valve-gears this will heat but 
one end of the cylinder, but where the valves can be operated by hand 
the steam can be admitted for warming to both ends, and the whole 
mass of metal brought up to the necessary temperature. It is desirable, 
however, to leave the drip-connections from the cylinder open until 
after the engine has started. The cylinder being fully warmed up, 

753 



754 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

which will be recognized by touch and by the high temperature of the 
drip-pipes, a little more steam can be admitted either through the 
wider opening of the throttle-valve, or through the more ample move- 
ment of the distributing-valves, so that sufficient pressure comes on 
the piston to start the engine. It becomes a matter of importance to 
store sufficient energy in the fly-wheel to carry it past its first dead- 
center, on which otherwise it would be likely to catch, and particularly 
if there is water in the cylinder whereby its motion can be arrested just 
at the time of getting ready to pass the center. If this difficulty is not 
met, the engine will then take up its regular motion, slowly at first, 
until all danger from water shall be passed, and then gradually more 
steam is admitted until its regular rate is reached, at which its governor 
will take hold and control the supply of steam. The danger from the 
water of condensation is usually passed at the end of two or three com- 
plete strokes, but it may last longer, and it may occur from priming 
even under regular service. The drip-valves are therefore closed 
cautiously, to be sure that all water has been blown out. It will make 
its presence manifest by a characteristic snapping or cracking like the 
blows of a metallic substance within the cylinder, which once heard will 
always be recognized. The danger from water has already been 
alluded to. If the engine is one requiring its cut-off to be regulated by 
hand, and not by the governor, as in link-motion engines, adjustable 
cut-off engines, etc., the throttle- valve will usually be opened wide and 
the regulation effected by the use of such adjusting mechanism when 
the normal speed of the engine is attained. 

537. To Start a Condensing Engine. Here again the variety of 
methods used to effect condensation makes it difficult to include all 
conditions (Chapter XXXI). If the engine is surface condensing, the 
circulating water will be started in motion before the main engine is 
started. If it is a jet-condensing engine driven by independent air- 
pump connections, the vacuum in the condenser will be created before 
the main engine is started by starting the independent air-pump. 
With the attached system or the gravity or siphon systems the vacuum 
must be created after the first steam is delivered to the condenser. 
With the attached system and large air-pump it is desirable to start 
the engine with the crank in such position that the first motion of the 
piston shall cause the working stroke of the pump to take place and 
create a partial vacuum in the condenser. Sometimes the vacuum is 
created in advance of starting the attached mechanism by permitting 
the condenser to fill with water, and attaching an independent pump 
to the condenser which shall draw out the water until its capacity for 
equahzing pressures in its own cylinder and the condenser are reached. 



CARE AND MANAGEMENT. ACCIDENTS 755 

In many cases the cool metal of the condenser will serve to effect the 
first condensation and create a sufficient initial vacuum for the engine 
to get its air-pump to work without difficulty. The drip-connections 
of a condensing engine are different from those of a non-condensing 
engine, because as soon as the engine has started, the flow would be into 
the cylinder through them. For this reason they are either left off or 
are connected into the condenser piping. After the engine has turned 
its centres, the handling of its condensing appliance will involve the 
control of the inject ion- water in jet or direct-contact condensers and 
the speed of the circulating-pumps in the surface type. Since it may 
happen, in condensing arrangements where the air-pump and circu- 
lating-pump are driven from ihe same rod, that the full capacity of the 
circulating-pump is not required, while the air-pump must work full 
stroke, a by-pass valve is usually made on the circulating connections, 
so that it shall be able to pass its own water round and round in part, 
and not be compelled to handle an unnecessary weight to effect con- 
densation. The injection of jet condensers enters them by atmos- 
pheric pressure, so that the valve which controls need not usually be 
wide open. The operation of the condenser is regulated by the reading 
of the vacuum-gauge, which is graduated either from zero to 15 pounds 
of vacuum, or from zero to 30 inches of mercury. The vacuum is 
satisfactory if it reads over 13 pounds or 27 inches. It will be less than 
this either if water is sufficiently in excess to overfill or drown the 
condenser, or if there is too little water to dispose of all the heat which 
the steam brings into the condenser. 

538. To Start a Compound Engine. The compound engine, having 
l)oth a non-condensing and a condensing cyUnder, requires to be 
handled in starting according to the principles laid down in both the 
previous paragrafs. It is usual, however, to derive in the compound 
engine an advantage in starting which is not present in the single engine. 
If the two cranks are at an angle with each other, which is usual in 
power-house practice, it becomes possible to start the engine, even if 
the first or high-pressure cyUnder stands, with its crank on the dead- 
centre. A valve connecting the receiver of the low-pressure cylinder 
with the steam-pipe will be controlled by a valve which will be called 
the by-pass valve. By opening it, boiler-steam is admitted directly 
to the low-pressure cylinder, which will be at its best mechanical advan- 
tage if the high-pressure crank is at its dead-center, and by these means 
the engine can always be started either as a low-pressure or as a high- 
pressure according to the position of the cranks. The complication of 
the steam-heated receiver and steam-jackets adds nothing of diflSculty 
to an engine of this sort. The jackets make it unnecessary to pay 



756 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

special attention to the heating of the cyhnder, since to open steam on 
the jackets will accomplish this purpose. Some recent practice has 
attached the steam-pipe of the independent air-pump to the jackets 
and receiver-circuits, so that the steam must be turned on to the 
jackets for warming the main cyUnder before the engine is started. 
This is desirable to guard against the possibility of difficulty caused by 
unequal expansion of parts which are hot and cold. 

The compound locomotive with intercepting-valve operating auto- 
matically starts just like the simple engine non-condensing. 

In large vertical engines such as are used in marine practice, where 
the engine is on different levels, it is often necessary to have several 
hands for proper starting. Usually one level is the working platform 
in such cases. The common practice on board ship is that the chief 
in starting is at the throttle-valve, the first assistant in charge of the 
valve-gear, and while the second is in charge of the fire-room, the third 
or junior will take the bell or signalling apparatus from the bridge. 
In large engines fitted with a barring engine (paragraf 410) the start- 
ing is particularly simple, after the cylinders are warmed. It is a matter 
of many minutes to warm up and start a large multiple-cylinder engine 
by reason of the danger from water in the cylinders and it cannot be 
hurried. Twenty minutes or so should be allowed, a fact which has a 
bearing upon emergency calls upon such engines for fire or other similar 
uses. 

539. To Start a Steam Turbine. In the steam turbine the danger 
from starting with the casings too cool is not from the condensed water, 
but from unequal expansions, and hence a lack of balance when the 
rotor gets to speed. Steam is first turned on and blown through with 
the rotor at rest. The auxiliaries are started while the heating is in 
progress, first the circulating pump, then the hot-well and dry-air 
pump. It will take 10 to 15 minutes to start a large Curtis or Parsons 
turbine, or two or three minutes after it has become thoroughly warm. 
With a superheating apparatus, which usually becomes more effective 
as more steam flows through it after starting, it is necessary to prevent 
vibration due to unequal heating after the work comes on. The 
exciter set for the generator can be started after the rotor and generator 
are up to speed and running in balance. 

In stopping a turbine, after the steam is shut off, the condenser 
should be also, either by its valve or by stopping the auxiliaries. A 
turbine will run in a vacuum for 30 to 60 minutes after the load is off, 
but by admitting air through the drips this acts as a brake; or the 
load may be left on. 

In Curtis vertical turbine plants, the foot-step pump must be started 



I 



CARE AND MANAGEMENT. ACCIDENTS 757 

and its accumulator put in service before the rotor is allowed to 
turn. 

In electric stations which operate alternators in parallel the process 
of synchronizing the independent engines must also be a feature of the 
starting process, so as to get them in step and phase. Where there are 
glands on the rotor shaft for centrifugal water packing, it is sometimes 
difficult to start condensing by reason of the cold air leakage which 
takes place until the rotor is up to speed. This is not a serious trouble 
in any case, and can be avoided by starting non-condensing and then 
changing over. Or the glands may be allowed to leak until the load 
comes on, and have the gland water turned on then. With a turbine 
plant, the auxiliaries call for more attentive care than the turbine itself. 

540. Management of Engines. The operation of an engine which has 
been properly designed in the light of experience and application of 
scientific principles should consist only in keeping up the functions of 
each detail. The oiUng system and ail channels and ducts for oil 
should be kept open and free; the packings should be just tight enough 
to prevent leakage, and should be renewed when worn. The piston 
rings must be kept tight, and all lost motion in the joints taken up as 
it occurs from wear. The whole previous part of this treatise has been 
directed to make this service an intelligent one. 

The control of the operation of the steam in the cylinder under the 
action of valve-gear and governor is the point where economy is most, 
effected. The valves should be tight, and the governor and gear in 
high efficiency. Occasional tests are most effective to see that this, 
result is obtained, and computations made of the cost of the horsepower 
per hour from such test, as a check upon increasing losses. 

The loss of income from a shut-down or stoppage of the engine may 
so far exceed the cost of the power-plant or its annual operation charge 
in large undertakings that almost any expense is justified if its result 
is to keep the engine running during every working hour. It should 
be the object of careful management to prevent or forestall any shut- 
down. 

541. Shut-downs in the Engine Room. Major Accidents. A shut- 
down in the engine room may be the result of a disaster or accident, 
or of a mishap. The disaster is the breaking or wrecking of some 
element, and is only to be met by a replacement. Such are: 

1. The engine runs away and bursts the fly-wheel. 

2. Water in the cylinder cracks or breaks the cylinder or some part 
of the mechanism. 

3. A steam-pipe breaks or bursts, or a valve or some attachment on 
the pipe-system. 



758 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

4. Some element breaks from a defect in the material developed in 
use, or present from the start and hidden. 

When such a major accident occurs, a controversy nearly always 
follows as to the responsibility for it, or the proportion assignable to 
the designer who computed the strains, the builder who embodied the 
design in metal, the contractor or erecter who installed the machinery 
and the operator in charge. The second one is usually the only one 
for which the operator is exclusively responsible, and even here defect- 
ive designing can help greatly in bringing it about. The operator is 
responsible only for the first when the governing apparatus was inoper- 
ative from his fault; and for the third when it is due to water-hammer 
from careless handling of valves. 

In addition to these disabling accidents shut-downs may also be 
made necessary for short periods from minor accidents, more properly 
called mishaps. 

543. Minor Accidents or Mishaps in the Engine Room. The most usual 
thing which goes wrong is the overheating of a bearing, either from too 
tight fitting of the bearings (Chapters XXIII and XXIV), or by defective 
ahnement (Chapter XXI), or from the use of poor oil or too little of it. 
The hot bearing is first annoying from the excess of friction which it 
indicates, but after a short period of heating the parts expand, increas- 
ing the friction or hold which they have upon each other, whereupon 
the contact-surfaces begin to cut each other and the presence of the 
abraded material caused by such cutting occasions greater heating and 
finally destroys the contact-surfaces so that until refitted they will 
never run cool. For a revolving bearing which heats only moderately 
a wick or mat of some fibrous material which dips into a bucket of water 
•can be used upon the heating shaft. Most marine engines (where 
alinement is troublesome by reason of the flexibihty of the hull which 
carries the bearings) are fitted with special arrangements for carrymg 
a current of water to be discharged upon the bearings and keep them 
cool. When cutting has begun it can sometimes be arrested by using 
a lubricant of heavier body, or by compounding a lubricant by mixing 
tallow and graphite. If the bearing is very large and the cutting very 
serious, a mixture of tallow with lead-fihngs and powdered sulphur 
makes a compound which fills up the abraded surface in part, and often 
has prevented the cutting from going further until the bearings can be 
permanently refitted. Mercury may take the place of the lead. 

In an engine otherwise well designed heating may be due also to the 
concentration of the load upon too small an area. This is incurable as 
a fault in design, but the heating which has been referred to above is 
the type which is preventable. 



CARE AND MANAGEMENT. ACCIDENTS 759 

An engine may give trouble by a knock or pound at some part of its 
stroke. Probable causes for this knock or pound are: 

(1) The main shaft out of line, so that the crank-pin is not perpen- 
dicular to the cyHnder-axis (Chap. XXI). 

(2) Lost motion in the pin-joints (Chap. XXIII). 

(3) -Lost motion of the piston-follower, or of the entire piston on 
its rod by reason of the slacking of the nuts or keys (Chap. XXII). 

(4) The valve loose on its rod or within its yoke. 

(5) A shoulder in the cylinder, worn in the bore, which some change 
in the length of the mechanism causes the piston to strike. 

(6) A side motion of the piston forced against the side of the bore 
when the steam comes on a piston which overlaps the port. 

(7) An up-and-down motion of the piston toward the middle of its 
stroke by a deflection of the guides under the oblique pressure from 
the connecting-rod. 

(8) A loose guide, or the cross-head, does not have full contact 
against the guide at all points. 

(9) Defective proportion of the steam-pressure to the weight of the 
reciprocating parts, so that the effort of the steam does not reach the 
crank-pin until after the latter have been accelerated. Delayed admis- 
sion of steam produces the same effect. 

(10) Improper compression, so that the lost motion necessary in 
the bearings for lubrication is taken up upon the crank-pin instead of 
upon a steam-cushion in the cylinder. Excessive compression may 
lift the valve, whereby a knock occurs when the valve returns to its 
seat. 

The renewing of packing in stuffing-boxes of rods and stems is scarcely 
to be considered under the head of an accident, but belongs rather to 
the general maintenance of an engine in its proper working condition. 
In a special class also are accidents to the employees, due to their own 
negligence, or unavoidable by them. These of course do not belong to 
the class of accident or mishap to the machinery. 



CHAPTER XXXIY. 

TESTING THE POWER PLANT FOR ECONOMY AND EFFICIENCY. 

545. General. The testing of the power plant belongs to a depart- 
ment which has been called experimental engineering and whose 
practitioners have been called steam experts. It forms a field too large 
to receive more than general allusion in a treatise such as this. The 
object in any power plant will be to ascertain whether the energy 
supplied in the form of fuel and liberated as heat in the furnace is being 
utihzed as well as it might be, and with as great economy as possible; 
and further, to find, if such is not the case, at what points improvement 
and elevation of standard are to be sought. In a plant consisting of 
engine and boiler or a number of both it is obvious that there is an 
efficiency of the plant as a whole, and there is an efficiency of the boiler 
and efficiency of the engine separately. Such questions also come to 
the manager in control of a power plant when new appliances which 
are called improvements are presented for adoption. It is undoubtedly 
a stimulus to the operators of a power plant to know that at certain 
convenient intervals the efficiency of the plant is to be observed by the 
conduct of proper tests. 

Power-plant tests for economy and efficiency will involve tests of the 
boiler plant, and of the engine plant either together or separately. 
There is usually also an acceptance test to ascertain if the guarantees 
and the specifications have been complied with and met. 

546. The Boiler Test. The boiler test is made to secure the data for 
the heat balance (paragraf 144). In general terms this involves weigh- 
ing the water supplied to the boiler through the feed-pump in a given 
time, and the coal charged during that same time. The ash and incom- 
bustible matter withdrawn from the ash-pits are to be subtracted from 
the coal burned as a means of finding out the percentage of ash and 
crediting the boiler with the actual combustible supplied to it, and the 
steam passing off through the steam-pipe should be sampled at fre- 
quent intervals during the test to see whether it is delivering evapo- 
rated water in the form of steam, or is entraining water through the 
pipe of the engine without forming steam. It is obvious that to refrain 
from this check upon the quality of steam is to credit the boiler with 
evaporating more water and disposing of more heat than it actually did, 

760 



ECONOMY AND EFFICIENCY 761 

and therefore to increase in the result the amount of water really and 
effectively handled by the boiler in a given time. The weight of coal 
charged into the furnace is determined by scales of any reliable structure 
which will read to a quarter of a pound, and the weight of water by 
having two tanks similarly mounted on scales into which the suction- 
pipe of the pump can be placed alternately, and the weight of water 
fed determined by the difference between the initial and final readings 
as each tank is alternately filled and emptied. It is usual to have an 
observer specially detailed for the coal and the water scales, with blanks 
upon which he makes the entries as observed and which form the log 
of the test. Meters may be used to check the weighings. 

547. Flue-gases. It is desirable in a boiler-test to know whether 
the products of combustion escaping from the setting are carrying an 
unnecessary amount of heat to waste, and whether the furnace-gases 
are of proper constitution with respect to waste of fuel in them or excess 
of oxygen reducing the temperature in the furnace. The temperature 
of the flue-gases can be observed by a standard pyrometer, if such are 
at hand; or a very close result can be obtained by the method with a 
ball or mass of iron inserted in the flue until it acquires the temperature 
of the gases, and then cooled in a known weight of water whose rise of 
temperature in cooling the mass of iron is observed. The volume of 
the flue-gases or the weight of the products of combustion can be 
ascertained from the readings of a gauge introduced so as to deter- 
mine the difference of pressure within the flue and outside of it. The 
composition of the chimney-gases is determined by gas-analysis methods, 
the best known apparatus being that of Orsat. Such appliances are 
specially directed to determine the amount of carbonic oxide, carbonic 
acid, and oxygen. 

Coal calorimeters for observing the calorific power of the fuel have 
already been referred to in paragraf 287. 

548. The Calorimeter. There are several forms of calorimeter 
which are used to determine the quality of the steam or the percentage 
of moisture which it contains, in order to correct the record of the 
scales which weigh the feed-water. These instruments withdraw from 
the main steam-pipe a sample of the steam which is passing through it 
by means of a nipple which crosses the pipe, and suitable perforations 
in it withdraw the material which is passing through the pipe at all its 
sections. The material drawn out through such a nipple is then 
analyzed by the calorimeter proper of which there are many forms. 

The most accepted of current practice is a combined separating and 
throttling calorimeter, in which the water in the sample taken from the 
pipe is first separated, and then the steam analyzed by passing it 



762 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

through a throttle orifice whereby it becomes superheated. The heat 
necessary for evaporating the water which it contains is measured by 
the difference in reading of thermometers inserted into the instrument. 
Other types of calorimeters are the coil-calorimeter, in which the 
determination of the percentage of moisture is based upon the amount 
of heat necessary to condense the mixture which passes through a coil, 
and the barrel-calorimeter, in which a sample of the mixture from the 
nipple is taken into the -barrel of water through a flexible hose for 
similar condensation. The determinations are made by observing the 
difference in the heat-units required to condense the mixture as com- 
pared with what would be required if it was altogether steam. 

549. Report of a Boiler-test. The imiportance of a reasonably close 
agreement in methods for the conduct of a boiler-test have induced 
engineers to attempt to agree upon such standard methods, and a 
uniform method of tabulating and reporting them, together with the 
calculations which are involved in making the deductions from a boiler- 
test. The headings of such a standard form of report will be found in 
the Transactions of the American Society of Mechanical Engineers, 
to which those interested are referred.* The points covered are the 
dimensions and proportions of the boilers and furnaces, pressures, 
temperatures, analysis of fuel, ash quantities, calorific power of fuel and 
quantities, steam quality, water weights fed, horsepower developed, 
economic results, efficiency, cost of evaporation, smoke data, methods 
of firing, gas analysis, and include eighty -eight separate headings for 
a complete treatment. In the Appendices of the Committees' Report 
are many valuable data and suggestions. 

550. The Engine-test. It has already been made apparent (para- 
grafs 6 and 7) that for many engines the resistance appears in a form 
in which it can be directly measured, so as to determine the net or 
effective work received from the engine. Such cases would be where 
the work of the engine is pumping or hoisting, or the generation of 
electric energy. In many cases, however, where the resistance of the 
engine consists in driving the transmissive machinery of large establish- 
ments, the net resistance is not directly measurable, and the only 
method of determining the power and work of the engine is by means 
of measurements made upon the effort in the cyUnder. Moreover, 
under many circumstances the insertion of the measuring apparatus 
between the motor engine and the net resistance would be inconvenient 
or impossible. This hmitation of direct measurement is often imposed 
by the magnitude of the units involved, if for no other reason. If 

* Transactions Am. Soc. Mech. Engrs., Vol. 21, 1899-1900, Paper No. 827. Address 
for separate copies No. 29 West 39th St., New York, N. Y. 



a 



ECONOMY AND EFFICIENCY 763 

the power is small enough to be conveniently determined by direct 
measurement, the apparatus used for this purpose will be called a 
dynamometer. If the work is to be measured in the engine-cylinder, 
the instrument used will be called an indicator. 

For detailed discussion of dynamometers of the absorption and 
transmitting types, and for the discussion of the indicator, its forms 
and calibration, the reader is referred to admirable special treatises. 
The treatments in paragrafs 3, 295, 302, 304, 305 should have made 
clear what deductions can be made from the indicator diagram. 

The American Society of Mechanical Engineers in 1902-03 formulated 
also a standard code for the Testing of Engines, along lines similar to 
those for the conduct of tests of boilers.* It covers dimensions of the 
engine, boilers and auxiliaries, quantities of water, steam, and coal, 
pressures and temperatures, heat measurements, data of the indicator 
diagrams, speed, power, efficiency results, and ratios, and special data 
needed for tests of special types of engine or for particular services. The 
full report covers 121 headings. The preamble and appendices have 
also much important scientific and practical information, carrying its 
scope beyond the limits of the present treatment. 

* Transactions Amer. Soc. Mech. Engrs., Vol. 24, 1902-03, Paper No. 973. 



PART VIII. 
CHAPTER XXXV. 

GENERAL REMARKS UPON THE POWER PLANT. 

555. Concentrated or Subdivided Steam-power. There are two 
policies possible in the design of a power plant where the resistance to be 
overcome is extended over a large number of units, tools, machines, or 
whatever. The power may be liberated from the fuel in a central 
location and transformed into motor energy in a large engine near the 
boiler plant, and from this large engine power may be transmitted by 
shafting and belting all over the plant for use as required. The other 
plan is to carry the power in the form of steam or other energy to a 
large number of small steam-engines or motors located at convenient 
points and each of which drives its own section or group of machines. 

There is no question as to the wisdom of concentrating the generating 
or power-furnace plant, whichever of the other two systems be con- 
sidered advisable. The reason for this is that the handling of fuel and 
of ashes and superintendence of the boiler plant is made economical in 
proportion as the number of these units is large when they are con- 
centrated under one superintendence and in one place. The fire-risk 
and insurance problem is also diminished by the scheme of concentra- 
tion. It becomes of advantage to use mechanical methods for handling 
fuel where large numbers of horsepower are concentrated and where 
one mechanical plant can serve for them all. The cost of stack or 
artificial-blast appliance is less per unit when they are together. 

Much the same arguments are to be urged for the principle of driving 
the plant from one central engine. The concentration of supplies, 
repairs, and superintendence, which will vary with the number of 
engines and not with their size, all point to the advantage of this system, 
as in the case of the boiler plant. There is the further advantage that 
the large engine will be more economical in proportion than the indi- 
vidual small ones, furnishing in the aggregate the same amount of 
horsepower. This is one of the arguments for the central-station 
method of furnishing power for street-railway propulsion rather than 
by individual motors. With the central engine the loss in transmitting 
its power by shafting, belting, or similar means to the individual and 
subdivided machines is a loss in friction; and furthermore, with some 
exceptions it will be necessary to drive the whole plant of transmissive 

764 



GENERAL REMARKS 765 

machinery in order to run a small section of it for work overtime or 
where it must not be intermitted, as in the boring of cylinders and such 
work. Moreover, the failure of the central engine or any part of the 
transmission machinery makes it necessary to stop the entire estab- 
lishment. With subdivided power only the part affected need be iso- 
lated for repair, while the rest runs on without interruption. 

With the system of subdivided power among small engines the trans- 
mission loss is from condensation of steam in the pipes which connect 
the boiler plant to the various engines, which is probably, with an 
efficient system of non-conducting coverings (Chapter XIV), less 
than the loss- by friction expressed in percentage of the whole power 
furnished to the piping system. This plan furthermore has the 
advantage that only the section of the plant which is desired need be 
run for overtime or special work, and the system is further flexible if 
it is desired to run one engine with its attached machinery at higher 
speed or slower than the normal. The aggregate first cost of the 
number of engines, if of the same character as to workmanship as the 
single large engine, when the cost of foundations and pipe and of drip 
and exhaust connections is added, is likely to exceed the first cost of 
the large engine. On the other hand, the whole power from the plant 
does not have to pass through the first set of transmissive shafting, but 
the principle of subdivision enables each section of shafting and its 
corresponding pulleys to be lighter in proportion, diminishing the fric- 
tion which is caused by weight, and failure of one engine or main belt 
does not arrest the whole plant. 

556. Distribution of Power by Electricity, Gas, or Air. In addition 
to the methods of transmitting power by steam or shafting discussed 
above, the methods of distributing by other transmission systems 
should be considered. The first plan is that of using an electric genera- 
tor in connection with one or more central engines, from which the power 
will be distributed by wires carrying the current to the sections driven 
each by its own independent motor, or to separate machines each with 
its own motor. The cleanliness, convenience, compactness, and easy 
control of the electric transmission makes it very attractive, and the 
loss in the conversion of the steam energy into electric energy and its 
transmission and reconversion into motion are apt to be about the same 
as the losses in friction in high-grade plants, and will be less than such 
losses where settling or careless management has permitted the trans- 
missive machinery to deteriorate in quality. If but one generator is 
used, there is the same difficulty as with the central .engine in the pre- 
vious paragraph, that a breakdown of that central engine stops the 
entire plant; but this can be met by either dupUcate engines, or by the 



766 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

principle of subdivision in the power house, where the aggregate of 
several units makes up the entire source of energy, and they are not 
likely to fail all at once. The expense of multiplying motors must be 
considered in this system, although it must not be forgotten that with 
it the cost of shafting, hangers, and pulleys does not have to be incurred, 
and serves to offset the cost of motors. Moreover the whole shafting 
does not have to be run for a few tools ; and no power is wasted for any 
tool or machine while not actually running. This may be a large 
proportion of the time of working days. 

Only since the commercial problem of the storage of electrical energy 
has been successfully solved, have electrical transmission systems 
ceased to offer the same objections which belong *to the preceding plans, 
that there is no storage of energy when not wanted, to be given out 
when it is called for. This is a great advantage which is offered by the 
use of gas-engines operated by gas made in a producer and stored in a 
holder. The gas-engine operates only when wanted and when gas is 
shut off from it all expense connected with it stops except interest. 
Gas can be made at maximum efficiency for a short period, and then 
the expense connected with its generation stops until the supply is 
exhausted. The system possesses all the other advantages of sub- 
divided power. 

The distributing of power by compressed air for motors has not been 
widely extended by reason of the usual absence of any conditions which 
make the use of the exhaust-air convenient or desirable at the place 
where it is discharged. In mining practice and similar places this is 
an immense advantage for compressed-air machinery, which is further- 
more clean and convenient. There is a loss in the double conversion 
at the air-compressor in the power house, and the reconversion at the 
air-engine, which is only to be offset by the use of extra heating appli- 
ances at the motor whose cost must be charged to the method of trans- 
mission. This in no way is to be considered as an argument against the 
convenience of compressed air for many machines of the portable or 
detached character. 

557. Location of a Power Plant. The choice of a location for a power 
plant is often fixed by considerations over which the engineer has no 
control. When such control is possible the considerations directing 
the choice of a location are mainly those of good sense and experience 
with respect to some of the following points: 

(1) It must be accessible for the dehvery of the fuel-supply and for 
the removal of ashes. In cities with a waterfront so that coal can be 
carried directly into the storage-bins from boats a considerable saving 
in cost per ton is to be effected, and this points to the selection of such 



GENERAL REMARKS 767 

water-front when otherwise convenient and possible. In the absence 
of water-transportation, the railway and the possibility of use of sidings 
from it are important features. It has already been discussed (Chapter 
XIII) that the delivery of coal into a boiler-room by gravity dimin- 
ishes the cost of a plant, but the fuel can as well be elevated within 
the power plant as without it. In cities where the transportation 
within the streets may be interrupted by the winter snows it is impor- 
tant that a sufficient storage capacity should be supplied in the plant to 
prevent possibilities of stoppage if there should be any interruption of 
regular transportation. In Figs. 691 and 692 are presented two typical 
large water-front power plants from the practice of New York City, 
which well deserve critical and careful study in details of arrangement 
and planning to meet the obstacles of their enforced location. 

(2) The water supplied to a power plant is a vital question, and a 
disregard of it in advance has often increased the operating expenses 
considerably. In most cities the water for a power plant is metered 
from the city or water company's mains, so that a fixed charge per 
annum for water is an element which must be considered. If conden- 
sation is to be effected, a supply of water for this purpose is also required, 
and in a large plant it becomes a very considerable quantity. ' It is 
quite usual to obtain this water of condensation from wells sunk within 
the grounds of a power plant, and a nearness to large bodies of water 
in streams or rivers is of manifest advantage in this respect. It is 
often found that well-water either from deep artesian wells or the 
driven-well sources is apt to contain matter deleterious to boilers, 
rendering such water unfit for steam-making. References to methods 
for saving water used in condensation have been given in Chapter 
XXXI. 

(3) Proximity to the water-front or the railway often favors the 
third element in selecting a location, which is to find a place where 
the smoke from the furnaces discharged through the chimneys shall 
not make the power plant a nuisance in the view of the neighborhood. 
The large chimney-stacks, if that method of draft is chosen, are useful 
rather than ornamental outside of the industrial district of cities; and 
if by the use of artificial draft or from the nature of the power plant 
(paragrafs 284 to 286) there is noise within it or an unpleasant 
vibration caused by the engine exhausts or other reciprocating motion, 
it may give rise to obstacles, legal and otherwise, to the satisfactory 
operation of the plant. 

(4) The securing of draft from the chimney-stack, if natural draft 
is used, must be sought by locating the stacks in such a relation that 
surrounding conditions shall not prevent their satisfactory working. 



768 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

High buildings either in the Hne of prevailing winds to windward or to 
leeward of a stack will make conditions unfavorable to it. 

(5) The cost of the ground is also likely to be affected by the location 
chosen with regard to the previous conditions, but in their absence it 
cannot be disregarded. It is usually to be foreseen that the power- 
plant will grow with the increased demands which are likely to be put 
upon it, and the obtaining of the necessary land for such growth is a 
matter to be considered to some extent in location. 

558. Construction of a Power House. The construction of a power 
house will be conditioned very largely by the price of land and the 
ground which it may be allowed to cover. If ground is not expensive 
there are great advantages in making the power plant all on the ground- 
level, both engines and boilers. It is desirable not to put them in the 
same room with no separating partition, by reason of the heat and 
dust which the fires cause and the moisture in the air which comes 
from leakage and evaporation. If the boilers and engines must be 
under one ro6f, a separating partition with as few door-openings as 
possible is necessary. It is desirable on account of fire-danger to 
keep the engines and boilers within separate fire-walls. 

If ground is too costly to permit this arrangement, the boilers and 
engines must be arranged vertically in successive stories, and it becomes 
a question whether to put the great weight of the stationary boilers 
on the ground or in a basement, and the lighter weight, but moving 
masses, in the upper layers, or to reverse this arrangement. The older 
plan was to put the boilers and coal below, and the engines above. It is 
interesting to observe the reversal of this system in some modern power 
plants in the larger cities where ground must be economized. The 
revolving machinery is put in the basement on the ground, where its 
vibration can produce the least effect upon the walls and floors. The 
dead load of the boilers and their contents is borne upon the next tier 
of floors, and the coal-bins are put at the top of all with elevators or 
hoists to fill them conveniently from the street-levels. This offers 
manifest advantages in economy of handling material, and the only 
objection to be urged is the slightly diminished effective height of 
chimney which is caused by elevating the boilers. 

The construction of the power house will be conditioned somewhat 
by the foregoing principles. If it is a smgle-story building, the ordinary 
construction of brick walls with proper foundations and a Ught iron 
roof is the typical and approved design. It is, however, exceedingly 
convenient in the power plant to have it commanded by a traveUing 
crane spanning from wall to wall, so that the rapid handhng of machinery 
in case of repair or substitution or extension is possible with such 




Fig, 691. Cross-Section, Manhattan RAiLWA-ii|p^, 
George H. Pegram. Ch. Eng'r; W. E. Baker 




C ipany's Power Station, New York City. 

\\ L. Eng'r; L. B. Stillwell, Elec. Eng'r. 




A^:-.^^V ; r..r};J-A ^ #- -'^ 



Metropolitan Street Railway Company, New Yoi 

9. S. PIERSON, CONSULTING ENGINEER. 



3: 



i 



11 



GENERAL REMARKS 769 

facilities. In the two-story or many-storied power plant the con- 
struction becomes the more costly, by reason of the weight to be 
provided for per square foot of floor-space, and of the necessity for 
fire-proof construction and of the weights which come upon the walls. 
This opens a department of the subject with which the present hmits 
of subject and space make it impossible to cope, and which belong to 
the department of the structural engineer. In such a building the 
provision for growth by addition of engine-units is to be foreseen and 
provided for, since the limitations imposed by the wall-construction 
are positive and fixed. 

559. Arrangement of the Power Plant. It is a conceded principle of 
power-house practice for public use that the machines must be in whole 
or in part in duplicate, so that the failure of any part shall not necessitate 
an entire stoppage of the supply of power to users. If, therefore, the 
duphcation is only partial, the failure of some detail in those departments 
of which there is but one example may cripple the whole plant. It is 
usual to have spare boilers and spare engines in a large plant, but there 
are many in which there is but one steam-pipe, and in which a failure 
or accident to the pipe would be as fatal as to the motive machinery 
itself. Some of the best and newest power plants have everything 
duplicated, so that there are practically two plants in one. It is an 
advantage if the principle of subdivision in the plant itself is carried 
out to make the power units of different capacity, so that when the 
demand for power varies it may be made by running units of different 
size to their full capacity, which is their most economical working. 
This is better than to have large units but partly loaded and running at 
a disadvantage for most of the time. 

Where the plant is to be driven from a single engine by belts and 
shafting, the engine should be at or near the center of the length of the 
main line of shafting. This diminishes the weight of shafting and 
friction, because only half as much power has to be transmitted by the 
torsion of each half-length if the resistance is wisely distributed. This 
plan gives rise to a ground-plan w^hich develops into a capital letter H, 
the power plant being in the cross-bar between the two buildings. 

There are special details of construction belonging to power plants 
which drive electric generators, as to the use of iron nails in floors and 
walls, which belong specifically to that department. 

560. Fire Protection of the Power Plant. The structural methods 
to be observed in power plants with respect to danger from fire have 
been a special study by the insurance companies. The conditions in 
general are that whatever woodwork there is in the power house should 
be massive, and the least possible space left concealed where the fire 



770 MECHANICAL ENGINEERING OF STEAM POWER PLANTS 

might start and lurk undetected until it had acquired headway. The 
construction of fire-doors and shutters to prevent the passage of fire 
and flame through walls is also a matter of some importance. 

561. Floors of the Power Plant. The floors of a machine-shop or 
engine-room are very important features of the building. A concrete 
floor either of the ordinary construction or made of some of the pro- 
prietary materials is the suitable arrangement for the fire-room space 
where not exposed to cracking from heat of ashes and similar condition. 
It is usual to lay down a fire-brick pavement close to the boilers, and the 
hot ashes and clinkers should be kept upon it. Ordinary brick or 
flagstone paving-stones will be found in many places where cement or 
artificial stone is costly or inconvenient. It is desirable that the floor 
should be one on which an abundance of water can be used for washing, 
and which should be arranged to drain itself into suitable catchbasins 
and drains by the grades used. A brick or concrete floor is not desirable 
for a room containing machinery, by reason of the continual grit which 
is worn from the floor by treading on it, and which currents of air carry 
into the revolving bearings. 

For the engine-room a wooden floor in two thicknesses is quite usual. 
The standard basement floor of the fire-insurance companies is a two- 
inch plank tongued and grooved, and laid on asphaltic concrete, while 
above that the floor-boards proper, 1^ inches thick, are blind-nailed. 
For upper floors the plank is 3-inch. The upper surface is the part 
subject to injury from weights upon it, and can be removed when worn 
without disturbing the main floor-surfaces. The floor of an engine- 
room should be of a structure which shall not be slippery by reason of 
oil which may get upon it. In electric-power stations wooden floors 
are of special significance, because a brick or cement flooring makes a 
sufiiciently good electrical connection with the ground to make acci- 
dental contact with a dynamo dangerous to a man standing on such 
floor, while with wood he is adequately insulated. 

The subject of construction of industrial buildings is too broad a 
one to be more than hinted at in such a connection as the foregoing, 
and the interested reader is referred to more extended discussions for 
exhaustive treatment. 



APPENDIX I. 

HISTORICAL SUMMARY. 

B.C. 120. Hero of Alexandria describes a steam reaction- wheel in his Spiritalia 

seu Pneumatica. 
A.D. 1601. Giovanni Battista della Porta in his Pneumatics describes conden- 

sation of steam in a closed vessel as a means of lifting water. 
1615. Solomon de Cans (Les Raisons des forces Mouvantes) describes 

raising water by steam-pressure above it in a closed vessel, 
1629. Branca describes turning a wheel by jet of steam against vanes. 

1663. Edward Somerset, second Marquis of Worcester, describes in his 

Century of Inventions a separate boiler whose pressure was admitted 
upon water in a closed vessel. 
1680. Denis Papin invents the digester for boiling at high pressure. 

1680. Huyghens proposes a true cylinder with piston traversing it. 

1681. Denis Papin invents the lever safety-valve. 

1690. Denis Papin applies the piston to receive motor-pressure, the cylinder 

being also the boiler. 

1697. Thos. Savery pumps by forcing water up by pressure, and lifts water 

into the chambers by the vacuum caused by condensing. 

1698. Savery's first patent for a pumping-engine. 

1705. Papin applies lifted water to turn a rotating wheel. Uses internal 

fire-box boiler. 

1705-07. Thos. Newcomen and John Cawley, with Savery, combine separate 
boiler, cylinder and piston, and surface condensation. The Atmos- 
pheric Engine. 

1716-18. Dr. Desaguliers improves Savery engine by using jet condensation. 

1713. Automatic valve-gear attributed to Humphrey Potter. 

1718. Plug-tree valve-gear for pumps designed by Henry Beighton. 

1725. Leupold designs a high-pressure non-condensing engine. 

1730-58. Smeaton improves Newcomen engines. 

1763-64. James Watt repairs model of Newcomen engine at Glasgow University. 

1766. William Blakey proposes a water-tube boiler. 

17G9. Watt's patent of separate condenser. 

1781. Jonathan Homblower invents double-cylinder or compound engine. 

1782. Watt's patent of expansive working of steam and double-acting 

engine. 
1784. Watt patents parallel motion, governor and indicator. 

1799, Murdock invents the three-ported slide-valve. 

1800. Trevithick in England and Ohver Evans in America introduce high- 

pressure non-condensing engines. 
1804, Arthur Woolf combines two-cylinder engine of Homblower type with 

higher steam-pressure and Watt's condenser. 
771 



772 



APPENDIX 



1804. 

1821. 

1838. 

1840-42. 

1840-45. 

1841. 
1841-44. 



1849. 

1849. 
1854. 
1855. 
1856. 
1857. 
1859. 
1859. 
1859. 



1860. 
1860. 

.1860. 
1868. 

1872-73. 



1874. 
1883. 
1885. 

1892-94 
1896. 



John Stevens designs a sectional boiler. 

Julius Griffith designs a sectional water-tube boiler. 

S. Hall uses a surface condenser on S. S. Wilberforce. 

Stephenson link-motion introduced. 

Shepard & Co. of Buffalo introduce the plug- valve with loose 
spindle for steam-distribution. 

F. E. Sickles patents a drop or trip cut-off. 

Henry R. Worthington invents and introduces direct-acting pumps 
without fly-wheel and with valve thrown by stored energy in 
springs and by steam-pressure on auxiliary engine-piston: also 
later the duplex pump. 

Geo. H. Corliss introduces a trip-gear, combined with wrist-plate, and 
plug- valves. 

B-valve designed by Henry R. Worthington for pumps. 

Randolph & Elder introduce compound engine for vessels. 

Greene trip- valve gear introduced. 

Stephen Wilcox uses inclined water-tubes for a boiler. 

Charles T. Porter invents the central-weighted or Porter governor. 

Radial valve-gear proposed by Hackworth. 

Independent circulating-pump used for condenser of S. S. Moulton. 

John F. Allen invents a valve-gear having a variable cut-off with 
positive movement, and introduces the multiport principle, and in 
1863 makes it a balanced valve. 

Chas. T. Porter employs these inventions of Mr. Allen to make a 
high-speed engine with automatic cut-off. 

Charles T. Porter invents the isochronous spring-governor, using a 
spring with initial tension so as to exert a resistance which varies 
directly as the diameter of the circle described by the balls. This 
underlies the shaft-governor. 

Chas. B. Richards invents the first indicator in which the motion of 
the piston was multiplied. 

Hartnell of England patents control of throw of eccentric by revolv- 
ing weights balanced by springs, in plane of rotation of the engine- 
shaft, but moves eccentric from forward towards backward posi- 
tion, and not towards the center of the shaft, 

John C. Hoadley applies the balanced-spring shaft-governor to 
control the throw of a single piston-valve in an automatic cut-off 
engine by moving eccentric across the shaft and giving invariable 
lead but variable cut-off release and compression 

A. C. Kirk introduces triple-expansion in S. S. Propontis. 

Gustav DeLaval of Sweden introduces the nozzle steam turbine. 

C. A. Parsons of New Castle, England, introduces the compound 
steam turbine. 

Inertia-principle of governing developed by Francis M. Rites. 

Chas. G. Curtis of New York introduces the stage compound nozzle 
steam turbine. 



APPENDIX II. 

STEAM TABLES. 

566. For convenient reference in computations involving the 
properties of steam, the following tables are reproduced. 

Note. The data have been taken from the published work of Prof. C. H. Peabody 
except where otherwise stated. The data above 300 pounds absolute are not reliable 
where the specific heat has entered as a factor, since its value at these higher pres- 
sures has not been fixed by general acceptance. 

The columns after No. 5 have been calculated as follows: 

X = 1091.7 + 0.305 (^ - 32); 

g = 1 + 0.00004.^ + 0.0000009^2 in centigrade units, reduced to 
Fahr. ; 

r = X~q = Col. 6 -Col. 7; 
r,= r-^ =Col. 8-Col. 10; 

Col. 10 = (Col. 1 X 144) X Col. 4 - 778; 

T 
Col. 11 = Spec. Ht. X Hyp Log— (see table, paragraf 567); 

^ , Column 8 _ , , L , 

Col. 12 = -— h Column 11; or ^s = — + 9^^ • 

Column 3 T 



773 



774 



.APPENDIX 



Pressure 
in Pounds 
by Gauge. 


- 


! 


<N t^ t^ t^ 


t^ t^ t^ t^ !>. 


t^ t^ CO CO 


CO CO CO CO CO 


CO CO 


-* CO cq ^ 

1 1 1 1 


O O Tt< CO <M 

7 1 1 1 1 


1 1+1+ 


(M CO ■«»< to O 


to o 

T-( CO 


Entropy of 
Vapor. 


cq 




»0 lO 05 
C^ ■<*< CO CD 
»0 oo C^ 00 
O 05 Oi 00 


(M CO (M O t^ 

r-H ,-( ,-H CO »0 
CO •^ 00 !>• CD 
OO OO t^ t^ t^ 


00 to !>. t^ <M 

OO (M t^ CO ^ 
to to Ttl Tt< ""JH 
t^ t^ t^ t^ t^ 


r-l CO OS rtH OS 
to T-H CO <M CO 
CO CO <N <M O 
t>. t^ !>■ t^ t^ 


O to 

OS CO 
00 t^ 

CO CD 










','■'■'', 


' 














Entropy of 
Liquid. 


- 


og 


1329 
*1754 
2013 


CO CO (N e^ CO 

<M CO oo OS OS 
(M <M C^ C^ (M 


UD ^ (M CO (M 
CO OS (M -* OS 
O O i-t ^ r-i 
CO CO CO CO CO 


00 (M -"i^ CO OS 
(M 00 C^ CD CO 
CO CO CO CO to 
CO CO CO CO CO 


.3685 
.3811 










Heat 

Eqiiiv. ot 

External 

Work. 

778 


o 


IT 


00 OS <N 00 


oo t^ CO O "* 


t- OTh to 00 


O cq r»< CO to 


. CO o 


00 i-H ■"*• lO 
lO CO CO CO 


CO r^ o T-H i-H 

CO co^ t^ t^ 


i-H (M M <M (M 

t^ i^ r- t^ !>■ 


CO CO CO CO ^^ 
t^ !>• t^ 1>- !>• 


to CO 


Heat 

Equiv. of 

Internal 

Work. 


05 






1-* Oi ^ 


•>*l r-l -*l 00 lO 


■* to CO CO O 


CO CO CO o to 


CO CO 




^ ^ 05 

00 CO ■* 
05 05 02 


O CO 00 "^ ^ 

-* CO o o o 
OS OS OS OS OS 


OO to CO<M O 
OS OS OS OS OS 
00 oo GO QO QO 


t^ to CO T-H T^ 

00 oo oo oo t^ 

00 oo 00 00 00 


CO CO 
CO to 
oo 00 


Heat of 
Vaporiza- 
tion. 
r 
B.T.U. 


00 


a 


CO O r-H CO 


(M oo O 00 OS 


rH to t^ rH 00 


CO to CO CO o 


OS CO 


oo CO CO in 

to Tj^ (M ^ 

o o o o 


t^ O OS lO (M 

o C5 t^ r^ i>" 

O O OS OS OS 


O t^ to to (M 

1^ CO CO CO CO 
OS OS OS OS OS 


O oo CD -^ CD 
CO to to to Tjl 
OS OS OS OS OS 


oo CO 

CO CO 

OS OS 


Heat of 
Liquid. 

q 


t- 


c= 
O oc 


O ■* 00 


■* t^ OS lO t^ 


CO CO OS 00 r-i 


CO CO T-H OS i-H 


^ ^ 


0^*105 
t^ 05 O 


T-H O r-H CD O 

CM CO CD CD t^ 


TtH oo O -H to 

t^ t^ 00 oo oo 


oo ^ -^ CO OS 
00 OS OS OS O 

T—{l—tT-tl—<C<t 


OS oo 

1-H CSI 

CO CO 


Total 
Heat. 

A 


CD 


a 

c 


. CO ri O ^ 


CO to OS CO CO 


t^ 00 CO OS OS 


OS 00 i>- to ^-H 


coo 


CO oo O lO 
5 O T-H <M (M 


oo ^ O CM CO 
(M CO Tj< rJH TJH 


rti to CO CO t^ 

TJH >* ^ ^ Tfl 


00 OS O 1-1 to 
"* Ttl to to to 


oo ^ 

to CO 


p ( . 1 . 1 1 1 




1 1 . 1 . 1 . 1 1 t 


I ( . 1 . 1 . 1 I 1 


' ! ' ' 




Weight of 
1 Cu. Ft. 
in Pounds. 


LO 


c 
c 


5 00 05 CO -"^ 

> lo C5 r^ ■<* 

3 1— 1 C^ lO oo 


t^ CD ^ CD r-H 

O CD (M CD 1— 1 

1— 1 CO CO oo 1— 1 

^ ^ CO CSl CO 

o o o o o 


to O ■* CD l^ 
to O OS (M CD 
CO CD ^- oo O 
CO CO CO CO "* 
O O O O O 


t^ t^ CO CO crs 

O ■* oo CO OS 
CO to t^ O '-H 

"^ to -^ to CO 

O O O O O 


CO to 

t^ 00 

o o 










Volume of 

1 Pound 

in Cu. 

Feet. 


Tt< 


c 


> oo CO CO "* 


^ C^ CD 00 '^t^ 
CO (M --H oo 1-H 


cq OS <M to OS 

oo t^ -* i-H to 


Cq O O r-H CO 
CO O OS OS ^ 


OS to 

to t^ 


5 O -^ CO 00 
5 v,-! CO t^ n 
D CO CO 1— < 1— < 

3 


O CO 00 ^ C<l 
OS I^ CO CO CO 


OS l>- CD CO ^ 
CSI CSI (N CS| <N 


CO C^ O OS CO 
CO CO CO rH T-H 


CO ^ 


Tempera- 
ture, De- 
grees Ab- 
solute. 


CO 


o 


> O Oi t^ CSJ 

. t- CO 05 CO 


OS ^^ to oo 00 

t^ O OS TJH CD 


C3S t— O CO (M 
to <M t^ t^ O 


-^ O "* to -* 
1-1 ^ OS CO t^ 


I^ OS 

OS oo 


1 o (M CD <rq 

5 ^ CD oo O 
H lO lO to CO 


CO CO CO oo (M 

1— 1 CM to to CD 
CO CO CD CD CO 


CO O (M CO t^ 

CO i-^ r^ t— r^ 

CO CO CD CD CD 


O CO to 00 O 

oo oo oo oo O 
CO CO CO CD r- 


O OS 


Tempera- 
ture, De- 
grees Fail!-. 


(M 


o c 

CN C 

CO « 


05 J:^ (M 

5 05 C^ CD 


OS ^ to OO oo 

O CO C5 I>- OS 


OS !>. O CO (N 

OO to O O CO 


■* O "* to ■* 
"^ '^ Cq OS o 


1^ OS 

CO ^ 


> r-H CD r-l 

5 O CSl -^ 


CO C^ CO t^ r-H 
to CO OS OS o 
,_,,_, rt ,_, CO 


to Oi C^ CO CO 

O O '-H ^ -H 

CS CSJ CSJ C^ <M 


OS cq to r- o 

1-H CO CO Cq Tt< 
CO Cq CO CO CO 


O OS 
to to 
CO CO 


Pressure 
above Vacuum 

in Pounds 
per Sq. Inch. 


- 


ir 










































5 












?^ - 












c 


J «J. 












5G 


> 1-t <M CO 


rt< to O ^ (M 


CO "^ ■^ to CO 

1— 1 T-t I— 1 1— 1 1— 1 


t>- 00 OS o to 

1-1 T-( Tl CO Cq 


o to 

CO CO 



APPENDIX 



775 



Pressure 
in Pounds 
by Gauge. 


^ 


CO CO CO CO CO 


CO CO CO CO CO 


CO CO CO CO CO 


CO CO CO CO CO 


CO CO 


lO O to O lO 
CSI OO CO ->*< "* 


O to O ^ <M 
to to CO CO CO 


CO ■«*< to CO t^ 
CO CO CO CO CO 


OO C3S O 'rt (M 
CO CO t^ t^ t>. 




Entropy of 
Vapor. 


IM 


t^ ^ o '^ crs 

lO CO OO O CO 
CD O '^ M^ CO 
CO CO CD CO CO 


to OO to CO ■* 
t^ ^ CO to -^i 
(M <M 1— 1 T— 1 ,-H 
CO CO CD CO CO 


to CO CD CO t^ 
CO (M .-1 O OS 

CO CO CO CD CD 


t>- QO OS t^ (N 
00 !>. CO CO to 

o o o o o 

CO CO CO CO CO 


CO CO 

'^ CO 
CD CO 






Entropy of 
Liquid. 


- 


^ O 05 r-H t^ 
CSI (M O 05 CD 
<35 O '— 1 i-H (M 
CO -* "* -^ ■* 


t- (N '^i CO tr^ 
CO O CD t^ OO 
CO rt< -* -* ■* 


OS T-H (M -^ to 
OS -H <M CO Tt* 
>* to to to to 


t^ OO OS o —• 

to CO r^ OS o 

to to to to CD 

■* Tt< Tt< -* -rfl 


CO CD 


1 


Heat 

Equiv. of 

External 

Work. 

pu 

778 


O 


!>. (M t^ (M CO 


O "* t^ OO OS 


OS O r-l ,-1 (M 


CO CO "* "^ to 


to CO 


CO t^ t^ OO 00 

t~- t— l>- 1^ t— 


OS OS OS OS OS 
!>• !>• l>. t^ t— 


OS O O O O 
t^ 00 00 00 00 


o o o o o 

OO OO QO 00 CO 


o o 

00 QO 


Heat 

Equiv. of 

Internal 

Work. 


C5 


CO OO t>- OS t— 


to t- 1-* "* CO 


O CO to OS <M 


Tf OO T-t to 00 


<M to 


O -* 05 -* o 

lo -"^ CO CO CO 

00 OO 00 00 00 


CO C<I OS OO l>- 
C^ (M T— 1 .-H — 1 
00 00 OO OO OO 


t^ CO to --^ Tji 

00 QO 00 00 00 


CO <N (M r-H o 
00 00 OO 00 00 


O Oi 

^ o 

00 00 


Heat of 
Vaporiza- 
tion. 
r 
B.T.U. 


00 


O O ■* 1-t CO 


to rH 00 (M to 


CJS CO CO O "* 


t>. .-1 to OS CO 


t^ ^ 


t^ <N t^ CO 0> 

(M <M ^ ,-H O 


to (M OO 00 t^ 
OOOSOSOS 
OS OS OO 00 00 


CD CO to to -^ 
OS OS OS OS OS 
00 00 00 00 00 


CO CO <M .-* ^ 

o^ o^ o^ o^ o^ 

00 OO 00 OO 00 


o o 

OS OS 
00 OO 


Heat of 
Liquid. 


t^ 


■>*' CO (M CO OS 


(M <M OS 00 t— 


CO to -* CO (M 


T-( O 00 t-- to 


->*| ca 


CO CO O CO 1-H 
CO '^ «0 Ut) CO 
C^ <M (M <M (M 


t^ C^ CO t^ 00 
CO t^ lr~- !>. i>. 
(M <M (M (M (M 


OS O i-H <M CO 
t^ OO OO OO OO 
irq (M (M (M (M 


■rf to to CO t^ 
00 00 OO OO OO 
C^ (M <M C<> CI 


OO OS 
OO OO 

c^ c^ 


Total 
Heat. 


CD 


rt< CO CO -* (M 


t^ CO t^ O (M 


to OO O CO CO 


00 1-H CO CO OO 


^ CO 


CO lO t^ OS ^ 
CO CO CD CD t^ 


<M -* to CO CO 
t^ t^ t^ t^ 1^- 


CD CD t^ t^ t^ 
t^ t^ t^ t- t^ 


b- OO OO OO OO 

t^ t^ t^ t^ b- 


OS OS 
t^ b- 






Weight of 
1 Cu. Ft. 
in Pounds. 


lO 


"* t^ 00 OS OS 

CO I^- 00 OS o 
OS O ^ (>» '^ 

O 1-1 T-l T-H T-l 


OS 00 CO t^ OS 
,-H (M CO to t~- 
to CO t^ t^ t^ 


1-1 C^» CO to CO 
O C^ -"^t^ CO OO 


00 O 1-H CO "* 

O CO to t^ cs> 

OS OS OS OS OS 


cot- 

.-< CO 




Volume of 

1 Pound 

inCu. 

Feet. 


■ Tfl 


1>. -"^ CO CO 

t— OS 1—1 OS OS 
CO M -* CO o 


CO -* CSI ,-H T-( 
OO ■* CO OS c^ 
to »-H !>• CO CO 


•* OO to (M 1-H 

to OO M CO o 
to rtl T*H CO CO 


O <M to OS -* 
■* OO (M CD 1-1 
(M 1-1 1-1 O O 


^ OS 
CD O 
OS OS 


O OS 00 t^ t>. 


CO I© to to to 


ioioio»o»o 


lO to to to to 


■* -* 


Tempera- 
ture, De- 
grees Ab- 
solute. 


CO 


CO O lO CS 1— 1 
OO OS »o »o CS| 


b- ^H OO OO OO 
"^ rti O OS 00 


CO tH-o«Ot-^ 

t^ CO to CO (M 


CO OS CSl '^ lO 

O 00 t^ to CO 


to to 

1-1 OS 


r— TjH — H t^ CO 

C^ CO ^ ^ lO 

t- t- t^ t- t^ 


OO CO OO OO OS 
to CO CD CD CD 

t^ t^ t^ t^ t^ 


O i-H (M CO -^ 
t^ t^ t^ t^ t^ 
t^ t-- t^ I>. I>- 


to to CD !>. 00 
t^ 1>- t^ t^ !>. 


OS OS 

r- t- 

!>. t- 


Tempera- 
ture, De- 
grees Fahr. 


(M 


CO crs to 03 r-H 

1-1 (M 00 OO to 


t^ T— 1 OO OO OO 

t^ t^ CO (M r-( 


CD Tj< O CD »— 1 
O OS OO CD to 


CO OS M -^ to 

CO 1-1 O OO CO 


to to 


t^ -* O CD (M 

CO t^ OO cx) OS 
(N c^ ca c^ c^ 


t^ (M t^ OO OS 

OS O O O O 
C^ CO CO CO CO 


O O ^ (N CO 
CO CO CO CO CO 


•* to CD CD I-- 
CO CO CO CO CO 


OO OS 

CO CO 


Pressure 
above Vacuum 

in Pounds 
per Sq. Inch. 














- 




















o to o to o 

•<*( .^ VO to CO 


to O to CO l>. 
CO t^ t^ t^ t^ 


OO OS O i-H c^ 
!>• t^ 00 OO OO 


CO Tt* to CO t^ 

00 OO 00 OO OO 


OO OS 

00 00 1 



776 



APPENDIX 



Pressure 
in Pounds 
by Gauge. 


-H 


CO CO CO CO CO 


CO o o o o 


O OO o o 


O OOOO 


OO 


UO «0 l^ C» 05 

l>- 1^ t^ t^ t^ 


O lO O O lO 
OO 00 05 o o 


O lO lO o o 
(M (M CO iO CO 


>o O to o to 

CO t^ t^ OO 00 


II 


Entropy of 
Vapor. 


(N 


t^ OO 03 ^ Csl 

c<i T-i c o o:> 

CO <£> CO CO lO 


'sfH !>. 05 Cq <M 
00 '^i O '^ ^ 
Oi 05 05 OO 00 
lO »0 >0 »0 lO 


"* t^ OO T-H OO 
(M 0> '^ OO CO 

r- CO CO lo lo 

lO iO uo lO lO 


00 OO (M '-I to 
r-H OS OS CO CO 
to "* >* Tt< ■* 

to to to to to 


CO O 
<M 1-1 

to to 






^? II 
1.1' 


■ ^ 


CO CO CO CO CO 

CO -* uo CO t-- 

CO CO CO CO CO 

•^ -^ -<tl -^ -^ 


CO CO O Ol '— 1 
00 CO OO CO 1—1 
CO !>. t^ 00 05 


t^ -^ CO O O 
(M CD CO CO OS 
O O i— 1 <M CN 
lO lO lO lO lO 


OS t^ to <M OS 
T-H ^ !>. O C^ 

CO CO CO ■* "* 

to to to to to 


"* O 
to 00 

■<*< -^ 
to to 


■ 


Heat 

Equiv. of 

External 

Work. 

778 


O 


t^ l>. 00 OO 05 


05 Cq Tt< 05 T-H 


CD 00 I-H CD OO 


OS O ^ <M CO 


rt^ to 


o o o o o 

OO 00 00 00 00 


O 1-H T-H ^ (M 

OO OO 00 OO 00 


<N C^ CO CO CO 
OO 00 OO OO OO 


CO Ttl -^ -<*< Tt< 

00 00 00 00 00 


OO OO 


Heat 

Equiv. of 

Internal • 

Work. 


05 


05 CO CO r-H -* 


00 OO 0> "^ Oi 


t^ CO T-H O (M 


'"J^ CO OS 1-H to 


OO M 


00 OO t^ t^ CD 

o o o o o 

OO OC OO OO OO 


>0 Cq Oi T:t< T-H 
O O 05 Oi 05 

OO OO t^ l>- ir^ 


TJH (M 00 (M OO 
OO OO Ir^ t^ CD 
t^ t^ t^ i:^ t^ 


CO ■<+i <M ^ OS 
CO CO CO CO to 

t>. t^ t^ 1>- 1^ 


t^ CO 

to to 


Heat of 
Vaporiza- 
tion, 
r 
B.T.U. 


00 


coo ■* 0> CO 


t^ O CO CO o 


CO T-H (M CO O 


CO CO O CO 00 


<M t^ 


05 05 OO t^ t^ 
00 00 OO 00 00 
OO 00 00 OO 00 


CO -* i-H CO T^ 

00 OO OO r^ t^ 

OO OO 00 00 00 


t^ lO .-< »o c^ 

CO CO CO »0 lO 
00 00 00 OO 00 


O GO t^ to CO 
to "* '^ -"^ "^ 
00 00 OO OO 00 


(N o 

00 00 


Heat of 

Liquid. 

Q 


t^ 


O 00 CO -* (M 


O Oscoir- O 


^ ^ ^ o O 


Tti <N I-H .^ CO 


00 OS 


O O ^ <M CO 


-<*< 1^ ^ 00 (M 
(M <M CO CO CO 


^ ^ O OO CO 
<N <M CJ CO '^ 

CO CO CO CO CO 


to 00 o cq ■<* 

■^ ^ to to .to 

CO CO CO CO CO 


CO OO 
to to 

CO CO 


Total 

Heat. 

A 


«o 


CO OO O CO uo 


Ir^ 05 Oi O O 


t^ lO Cq CD O 




O CO 


05 Oi o o o 

t^ t>- OO 00 CO 


O r-i cq to CO 
GO GO OO OO OO 


OO OS 1-H CO lO 
OO GO OS OS OS 


to CO t^ It- 00 

OS OS OS OS OS 


OS OS 
OS OS 




Weight ol 
1 Cu. Ft. 
in Pounds. 


lO 


OO O ^ <M ■>*' 
lO 00 O <M "* 

O O T-H T^ ^ 

cq (M (M (M C<l 


lO ^ 00 CS5 lO 
CO t^ t^ OO CT> 
T-H (N CO lO CO 
(N <M <M <M (M 


OS CO »— 1 »0 i— 1 
O i-H (M CO -^ 
O ^ C^ CO 00 

CO CO CO CO CO 


to OS CO l>- OS 
rJH T^ to to to 

OS O 1-H (M CO 

CO •* -rt^ -"^ -^ 


T-H to 

CO CD 

■>* to 


1 


Volume of 
1 Pound 
in Cu. 

Feet. 


■<*< 


GO OO O <M »0 
lO O CO ^H CO 
00 00 t^ t^ CO 


05 CO CO c^ ^ 
1-H O O CO ^ 

CO ■<*< cq 00 i>- 


CO C^ r-( r-l CO 

<M -H —1 to O 
CO CM O t^ CO 


to O 00 OS -* 

CO t^ O "* OS 

. to ■* Tji CO c^ 


-* OS 

(M ^ 


-rj< r^ Ttl Tt< ^ 


TJH -^ -* CO CO 


CO CO CO (M (M 


<N <N IM (N <M 


(M <N 


Tempera- 
ture. De- 
grees Ab- 
solute. 


CO 


^ CO o t^ ■<** 

t^ lO CO O OO 


05 OO CO CO lO 
lO CSI OO lO t^ 


CO to CD 00 to 
t^ to OS to CO 


t^ CO -"^i 1—1 CO 
CO OS T-i CO '^ 


to to 


O 1-H (M CO CO 
00 00 OO 00 OO 
t^ 1>- t^ !>• !>• 


"* OO r-H 00 i-H 

OO 00 en Oi O 
t^ !>. l-^ t^ GO 


O CO 00 CO ^ 
1-H 1— ( 1— ( C^ CO 
OO 00 00 OO OO 


CO to 00 O (M 
CO CO CO ■* ■* 
OO OO 00 00 00 


■* CD 
00 00 


Tempera- 
ture, De- 
grees Fahr. 


(N 


-* CO o r- ^ 

O 00 CD CO ^ 


05 OO CO CD iO 
GO lO >— 1 OO O 


CO to CO GO to 
O 00 Cq OO CD 


!>. CO "*! r-H CO 

OS (M '^ CO t^ 


(M r^ 

00 00 


O O t— 1 C^ CO 

c^ Ol <N c<i oq 

so CO CO CO CO 


CO r^ ^ t^ '-H 
oq csi CO CO "* 
CO CO CO CO CO 


O (M 00 to o 
to to to CO t-- 

CO CO CO CO CO 


(N to r^ OS 1—1 
!>. t^ t"- 1:^ OO 

CO CO CO CO CO 


CO to 


Pressure 
above Vacuum 

in Pounds 
per Sq. Inch. 


- 




O i-H (M CO Tt* 
05 0> Oi 05 Oi 


lO O lO lO o 
OS O O T-H c^ 

1— 1 1-H 1— ( T-l 


to O O to to 
CO Tfi to CO r- 

T— 1 tH r-H T— 1 T-H 


O to O to O 
OO GO OS OS ^ 
T-H r-< T-l ,-i (M 


to O 
o ^ 
cq cq 



1 



4 



i 



APPENDIX 



777 



Pressure 
in Pounds 
by Gauge. 




O O to lO lO 
O --H CSl CO -<*< 
M M (M (M (M 


* 

to to to to to 

to CO t^ oo CO 
(M (M (M (M CO 


to to to to to 
GO CO oo CO oo 
CO -^ -^^ to to 


to to to to 

oo oo oo 00 
CO t^ 00 05 




(M 


CO CO 05 <N ''^ 

05 ■» r-H 05 CO 

CO CO CO C^ (M 
lO lO to »0 lO 


O to CO ^ CO 
CO ^ 02 t^ (M 

(M C^ ,-H r-H 05 

to to to to -"f 


CO ■* oo CO 05 
to to <M CO O 
00 t^ t^ CO CD 

^ ^ "^ Ttl ^ 


to CO 00 00 
00 05 (M ir^ 
Tt< CO CO <M 






Entropy of 
Liquid. 


- 


-* CO ^ lO t^ 

lO lO CO CD t^ 
lO «0 lO lO to 


00 t^ CD CO oo 

-^ oo cq CO t^ 
t^ t^ 00 00 oo 

lO to to to to 


CO (M CO 05 CO 
■^ to --H 1— 1 Cq 
O --H CO ■* to 
CO CD CD CD CO 


00 ^ ,_( 05 
!>. CO oo C^ 
CO oo 05 '— 1 

CO CO CO t^ 




Heat 

Equiv. of 

External 

Work. 

pu 

778 


O 


CO t^ 05 O <M 


<M CO Tfl "* 00 


^ t^ ,_, CO t^ 


T-H (M CO 00 


-* -^ -^ to to 
oo oo oo oo oo 


to to to to to 

oo oo 00 oo 00 


CO CD t^ t^ t^ 

oo 00 oo oo 00 


00 00 oo oo 
00 oo oo oo 


Heat 

Equiv. of 

Internal 

Work. 

ri 


05 


CO CO CO to t^ 


M t^ CO O I>- 


to ^ Ol <M CD 


(N <N CO to 


-^ i-H t^ •* r-( 

to to "* ■* ^ 


05 CO -"^t* (M 1— 1 

CO CO CO CO c^ 

t^ t^ t^ t^ !>. 


1-H (M CO CO 00 

1— 1 o oi oo t— 
t^ t^ CO CO CO 


to CO (M I-H 
CO to ■* CO 

CO CO CO CO 


Heat of 
Vaporiza- 
tion. 

r 
B.T.U. 


00 


C<I CO C<> to 05 


"* O t^ TJH to 


05 i-H O to CO 


CO ■* CO CO 


05 CO cq o^ CO 

CO CO CO Cq (21 

oo 00 oo 00 3b 


■* (M C31 1^ r^ 

<M <N 1— t ,-H O 

oo oo oo oo oo 


1^ O T— t CO CD 
05 00 00 1-^ CO 
Ir^ t^ t^ t^ t^ 


oo ^ o o 
to ■* CO (rq 
ir^ t^ !>. t^ 


Heat of 

Liquid. 

Q 


- 


O T-H O t^ ^ 


Ol oo CO 05 CO 


00 (M to .-1 <M 


Tf< 05 O CO 


i-H to '— 1 '^ oo 

CO CO t^ t^ t^ 

CO CO CO CO CO 


i-H to oo T-H CO 

oo oo 00 05 o 
CO CO CO CO -^ 


05 <M CO -«^ -^ 
r-H CO -rt^ to CD 

Tti ^ -^ ^ Tfl 


(M 00 -* 00 
oo 05 >-H (M 
■«4< -^ to to 


Total 
Heat. 


o 


C^ '^ C<l C^l CO 


CO CO CO CO I>- 


t^ CO to CO to 


t^ CO t^ I>- 


O >— 1 CO -^ to 
CM (M (M (M (M 


co r^ oo 05 CO 

(M <M (M (M C^ 


t^ --H -rt^ ir^ O 

<— 1 (M (M (M CO 

csi c^ c^ ca CSI 


tO O -rh 00 

CO •<*< -^ -* 
cq (M <N CN 

1-H 1— 1 r-l 1-H 


Weight of 
1 Cu. Ft. 
in Pounds. 


lO 


ex. CO CO CO ^ 
CO b- 00 C35 o 
CO oo T-H CO CO 
'^ ■<*< to to to 


oo O (M ■* to 
to CD CO CD t^ 


<M to O O O 
t^ 05 CS) ^ CO 

to to CO CO CO 

00 CJl O ^ (M 


O O O O 
O -^ GO (M 

t^ t— t^ oo 

Tj< CD OO O 






^^^ 


_ ^ ,_, Cv, 


Volume of 

1 Pound 

in Cu. 

Feet. 


f 


(M ^ oo "# to 
'^i to <M to oo 

^ o oj oo t^ 


(M oq t^ '^ to 

(M CD O to C^ 
t- CO CD to CO 


ir^ (M (M 05 O 
CO ^ '^ to Oi 
^ O Oi oo t^ 


O t^ <M O 

oo oi CO OO 

CD to to "^ 


(M <M .-H .-H .-H 




T-l r-l O O O 


O O O O 


Tempera- 
ture, De- 
grees Ab- 
solute. 


CO 


GO Oi i— t C5 t~- 

lO -^ T-H CO i-H 


to (M (M (M O 

to oo O r-H t^ 


O O O O o 

CD CO 1-1 Ca CD 


O O O O 
00 CO "* to 


00 Cq 00 ^H to 
-Tf^ to to CO CO 

00 00 00 00 oo 


oo 1— 1 to 00 cd 

CO t^ t— t^ 05 

00 00 oo oo oo 


to t^ oo oo 1-^ 

O T-H (M CO -* 

<^ Oi O^ Oi <Ji 


Tti O '^t^ l>- 
CD oo O O 
Oi 05 05 O 


Tempera- 
ture, De- 
grees Fahr. 


iM 


oo 05 T-( 05 t^ 
oo t^ -^ C5 ■* 


to C^ (M <M 

oo I-H CO -* O 


02 CO -* to 05 


T-H CD t^ 00 


t^ ^ r- o "* 

00 0105 

CO CO CO -^ -^ 


t~ 1-H -^ t^ <rq 

O '-H ^ r-( CO 
-* Tt^ -*! '^ ^ 


-^ CO r^ i>- CO 
^ to CO t^ oo 

Tt^ ■* •<* ^ TjH 


'^ 05 oo CD 
O i-H oo '^ 
to to to to 


Pressure 
above Vacuum 

in Pounds 
per Sq. Inch. 


- 




to to o o o 

^ (M ^ to CO 
(M (M C^ (M (M 


C=> CD O O O 
t^ oo 05 o to 
C^ <M (M CO CO 


O O o o o 
O to o to o 

Tt< -ti to to CD 


O o o o 
o o o o 

t^ oo 05 O 



778 



APPENDIX 



LOGARITHMS 



567. In arithmetical computations, the usual base of the system is 
10, so that X, the logarithm for a number m, will be the exponent to 
which 10 is to be raised to give the quantity m,ovx = log^^ m. In analyt- 
ical mathematical work, the base generally employed is not 10, but is 
represented by e, whose value is 2.71828 +. To convert common or 
Briggs logarithms into Napierian logarithms, the former are to be multi- 
plied by 2.3026. 

The equation of the hyperbola in the form xi/ = constant leads to the 

deduction that the area between the hyperbolic curve and its nearest 

asymptote cut-off by two ordinates parallel to the other asymptote and 

distant respectively from the origin by a and b will be proportional to 

b dx 

log — . Hence it will be true that the integral of — will be the hyper- 
a X 

bolic logarithm of x. To save trouble of conversion, a table is appended 

covering the usual ranges required. 

HYPERBOLIC LOGARITHMS 



No. 


Log. 


No. 


Log. 


No. 


Log. 


No. 


Log. 


No. 


Log. 


i.oi 


.0099 


1.30 


.2624 


1.59 


.4637 


1.88 


.6313 


2.17 


.7747 


1.02 


.0198 


1.31 


.2700 


1.60 


.4700 


1.89 


.6366 


2.18 


.7793 


1.03 


.0296 


1.32 


.2776 


1.61 


.4762 


1.90 


.6419 


2.19 


.7839 


1.04 


.0392 


1.33 


.2852 


1.62 


.4824 


1.91 


.6471 


2.20 


.7885 


1.05 


.0488 


1.34 


.2927 


1.63 


.4886 


1.92 


.6523 


2.21 


.7930 


1.06 


.0583 


1.35 


.3001 


1.64 


.4947 


1.93 


.6575 


2.22 


.7975 


1.07 


.0677 


1.36 


.3075 


1.65 


.5008 


1.94 


.6627 


2.23 


.8020 


1.08 


.0770 


1.37 


.3148 


1.66 


.5068 


1.95 


.6678 


2.24 


.8065 


1.09 


.0862 


1.38 


.3221 


1.67 


.5128 


1.96 


.6729 


2.25 


.8109 


1.10 


.0953 


1.39 


.3293 


1.68 


.5188 


1.97 


.6780 


2.26 


.8154 


1.11 


.1044 


1.40 


.3365 


1.69 


.5247 


1.98 


.6831 


2.27 


.8198 


1.12 


.1133 


1.41 


.3436 


1.70 


.5306 


1.99 


.6881 


2.28 


.8242 


1.13 


.1222 


1.42 


.3507 


1.71 


.5365 


2.00 


.6931 


2.29 


.8286 


1.14 


.1310 


1.43 


.3577 


1.72 


.5423 


2.01 


.6981 


2.30 


.8329 


1.15 


.1398 


1.44 


.3646 


1.73 


.5481 


2.02 


.7031 


2.31 


.8372 


1.16 


.1484 


1.45 


.3716 


1.74 


.5539 


2.03 


.7080 


2.32 


.8416 


1.17 


.1570 


1.46 


.3784 


1.75 


.5596 


2.04 


.7129 


2.33 


.8458 


1.18 


.1655 


1.47 


.3853 


1.76 


.5653 


2.05 


.7178 


2.34 


.8502 


1.19 


.1740 


1.48 


.3920 


1.77 


.5710 


2.06 


.7227 


2.35 


.8544 


1.20 


.1823 


1.49 


.3988 


1.78 


.5766 


2.07 


.7275 


2.36 


.8587 


1.21 


.1906 


1.50 


.4055 


1.79 


.5822 


2.08 


.7324 


2.37 


.8629 


1.22 


.1988 


1.51 


.4121 


1.80 


.5878 


2.09 


.7372 


2.38 


.8671 


1.23 


.2070 


1.52 


.4187 


1.81 


,5933 


2.10 


.7419 


2.39 


.8713 


1.24 


.2151 


1.53 


.4253 


1.82 


.5988 


2.11 


.7467 


2.40 


.8755 


1.25 


.2231 


1.54 


.4318 


1.83 


.6043 


2.12 


.7514 


2.41 


.8796 


1.26 


.2311 


1.55 


.4383 


1.84 


.6098 


2.13 


.7561 


2.42 


.8838 


1.27 


.2390 


1.56 


.4447 


1.85 


.6152 


2.14 


.7608 


2.43 


.8879 


1.28 


.2469 


1.57 


.4511 


1.86 


.6206 


2.15 


.7655 


2.44 


.8920 


1.29 


.2546 


1.58 


.4574 


1.87 


.6259 


2.16 


.7701 


2.45 


.8961 



APPENDIX 
HYPERBOLIC LOGARITHMS 



779 



No. 


Log. 


No. 


Log. 


No. 


Log. 


No. 


Log. 


No. 


Log. 


2.46' 


.9002 


3.02 


1.1053 


3.58 


1.2754 


4.14 


1 . 4207 


4.70 


1.5476 


2.47 


.9042 


3.03 


1.1086 


3.59 


1.2782 


4.15 


1.4231 


4.71 


1.5497 


2.48 


.9083 


3.04 


1.1119 


3.60 


1 . 2809 


4.16 


1.4255 


4.72 


1.5518 


2.49 


.9123 


3.05 


1.1151 


3.61 


1.2837 


4.17 


1.4279 


4.73 


1.5539 


2.50 


.9163 


3.06 


1.1184 


3.62 


1.2865 


4.18 


1.4303 


4.74 


1.5560 


2.51 


.9203 


3.07 


1.1217 


3.63 


1.2892 


4.19 


1.4327 


4.75 


1.5581 


2.52 


.9243 


3.08 


1.1249 


3.64 


1.2920 


4.20 


1.4351 


4.76 


1.5602 


2.53 


.9282 


3.09 


1.1282 


3.65 


1 . 2947 


4.21 


1.4375 


4.77 


1.5623 


2.54 


.9322 


3.10 


1.1314 


3.66 


1.2975 


4.22 


1.4398 


4.78 


1.5644 


2.55 


.9361 


3.11 


1.1346 


3.67 


1.3002 


4.23 


1.4422 


4.79 


1.5665 


2.56 


.9400 


3.12 


1.1378 


3.68 


1 . 3029 


4.24 


1 . 4446 


4.80 


1.5686 


2.57 


.9439 


3.13 


1.1410 


3.69 


1.3056 


4.25 


1 . 4469 


4.81 


1.5707 


2.58 


.9478 


3.14 


1.1442 


3.70 


1.3083 


4.26 


1.4493 


4.82 


1.5728 


2.59 


.9517 


3.15 


1.1474 


3.71 


1.3110 


4.27 


1.4516 


4.83 


1.5748 


2.60 


.9555 


3.16 


1.1506 


3.72 


1.3137 


4.28 


1.4540 


4.84 


1.5769 


2.61 


.9594 


3.17 


1.1537 


3.73 


1.3164 


4.29 


1.4563 


4.85 


1.5790 


2.62 


.9632 


3.18 


1.1569 


3.74 


1.3191 


4.30 


1.4586 


4.86 


1.5810 


2.63 


.9670 


3.19 


1.1600 


3.75 


1.3218 


4.31 


1.4609 


4.87 


1.5831 


2.64 


.9708 


3.20 


1.1632 


3.76 


1.3244 


4.32 


1.4633 


4.88 


1.5851 


2.65 


.9746 


3.21 


1.1663 


3.77 


1.3271 


4.33 


1.4656 


4.89 


1.5872 


2.66 


.9783 


3.22 


1.1694 


3.78 


1.3297 


4.34 


1.4679 


4.90 


1.5892 


2.67 


.9821 


3.23 


1.1725 


3.79 


1.3324 


4.35 


1.4702 


4.91 


1.5913 


2.68 


.9858 


3.24 


1.1756 


3.80 


1.3350 


4.36 


. 1.4725 


4.92 


1.5933 


2.69 


.9895 


3.25 


1.1787 


3.81 


1.3376 


4.37 


1 . 4748 


4.93 


1.5953 


2.70 


.9933 


3.26 


1.1817 


3.82 


1.3403 


4.38 


1.4770 


4.94 


1.5974 


2.71 


.9969 


3.27 


1.1848 


3.83 


1 . 3429 


4.39 


1.4793 


4.95 


1.5994 


2.72 


1.0006 


3.28 


1.1878 


3.84 


1.3455 


4.40 


1.4816 


4.96 


1.6014 


2.73 


1.0043 


3.29 


1.1909 


3.85 


1.3481 


4.41 


1.4839 


4.97 


1.6034 


2.74 


1.0080 


3.30 


1.1939 


3.86 


1.3507 


4.42 


1.4861 


4.98 


1.6054 


2.75 


1.0116 


3.31 


1.1969 


3.87 


1.3533 


4.43 


1.4884 


4.99 


1 . 6074 


2.76 


1.0152 


3.32 


1.1999 


3.88 


1.3558 


4.44 


1.4907 


5.00 


1.6094 


2.77 


1.0188 


3.33 


1.2030 


3.89 


1.3584 


4.45 


1 . 4929 


5.01 


1.6114 


2.78 


1.0225 


3.34 


1.2060 


3.90 


1.3610 


4.46 


1.4951 


5.02 


1.6134 


2.79 


1.0260 


3.35 


1 . 2090 


3.91 


1.3635 


.4.47 


1.4974 


5.03 


1.6154 


2.80 


1.0296 


3.36 


1.2119 


3.92 


1.3661 


4.48 


1.4996 


5.04 


1.6174 


2.81 


1.0332 


3.37 


1.2149 


3.93 


1.3686 


4.49 


1.5019 


5.05 


1.6194 


2.82 


1.0367 


3.38 


1.2179 


3.94 


1.3712 


4.50 


1.5041 


5.06 


1.6214 


2.83 


1.0403 


3.39 


1.2208 


3.95 


1.3737 


4.51 


1.5063 


5.07 


1.6233 


2.84 


1.0438 


3.40 


1.2238 


3.96 


1.3762 


4.52 


1.5085 


5.08 


1.6253 


2.85 


1.0473 


3.41 


1.2267 


3.97 


1.3788 


4.53 


1.5107 


5.09 


1.6273 


2.86 


1.0508 


3.42 


1.2296 


3.98 


1.3813 


4.54 


1.5129 


5.10 


1.6292 


2.87 


1.0543 


3.43 


1.2326 


3.99 


1.3838 


4.55 


1.5151 


5.11 


1.6312 


2.88 


1.0578 


3.44 


1.2355 


4.00 


1.3863 


4.56 


1 5173 


5.12 


1.6332 


2.89 


1.0613 


3.45 


1.2384 


4.01 


1.3888 


4.57 


1.5195 


5.13 


1.6351 


2.90 


1.0647 


3.46 


1.2413 


4.02 


1.3913 


4.58 


1.5217 


5.14 


1.6371 


2.91 


1.0682 


3.47 


1 . 2442 


4.03 


1.3938 


4.59 


1.5239 


5.15 


1.6390 


2.92 


1.0716 


3.48 


1.2470 


4.04 


1.3962 


4.60 


1.5261 


5.16 


1 . 6409 


2.93 


1.0750 


3.49 


1.2499 


4.05 


1.3987 


4.61 


1.5282 


5.17 


1 . 6429 


2.94 


1.0784 


3.50 


1.2528 


4.06 


1.4012 


4.62 


1.5304 


5.18 


1 . 6448 


2.95 


1.0813 


3.51 


1.2556 


4.07 


1.4036 


4.63 


1.5326 


5.19 


1.6467 


2.96 


1.0852 


3.52 


1.2585 


4.08 


1.4061 


4.64 


1.5347 


5.20 


1 . 6487 


2.97 


1.0886 


3.53 


1.2613 


4.09 


1.4085 


4.65 


1.5369 


5.21 


1.6506 


2.98 


1.0919 


3.54 


1.2641 


4.10 


1.4110 


4.66 


1.5390 


5.22 


1.6525 


2.99 


1.0953 


3.55 


1.2669 


4.11 


1.4134 


4.67 


1.5412 


5.23 


1.6541 


3.00 


1.0986 


3.56 


1.2698 


4.12 


1.4159 


4.68 


1.5433 


5.24 


1.6563 


3.01 


1.1019 


3.57 


1.2726 


4.13 


1.4183 


4.69 


1 . 5454 


5.25 


1.6582 



780 



APPENDIX 
HYPERBOLIC LOGARITHMS 



No. 


Log. 


No. 


Log. 


No. 


Log. 


No. 


Log. 


No. 


Log. 


5.26 


1.6601 


5.82 


1.7613 


6.38 


1.8532 


6.94 


1.9373 


7.50 


2.0149 


5.27 


1.6620 


5.83 


1.7630 


6.39 


1.8547 


6.95 


1.9387 


7.51 


2.0162 


5.28 


1.6639 


5.84 


1.7647 


6.40 


1.8563 


6.96 


1 . 9402 


7.52 


2.0176 


5.29 


1.6658 


5.85 


1.7664 


6.41 


1.8579 


6.97 


1.9416 


7.53 


2.0189 


5.30 


1.6677 


5.86 


1.7681 


6.42 


1 . 8594 


6.98 


1.9430 


7.54 


2.0202 


5.31 


1.6696 


5.87 


1.7699 


6.43 


1.8610 


6.99 


1.9445 


7.55 


2.0215 


5.32 


1.6715 


5.88 


1.7716 


6.44 


1.8625 


7.00 


1 . 9459 


7.56 


2.0229 


5.33 


1.6734 


5.89 


1.7733 


6.45 


1.8641 


7.01 


1 . 9"473 


7.57 


2.0242 


5.34 


1.6752 


5.90 


1.7750 


6.46 


1.8656 


7.02 


1 . 9488 


7.58 


2.0255 


5.35 


1.6771 


5.91 


1.7766 


6.47 


1.8672 


7.03 


1.9502 


7.59 


2.0268 


5.36 


1.6790 


5.92 


1.7783 


6.48 


1.8687 


7.04 


1.9516 


7.60 


2.0281 


5.37 


1.6808 


5.93 


1.7800 


6.49 


1.8703 


7.05 


1.9530 


7.61 


2.0295 


5.38 


1.6827 


5.94 


1.7817 


6.50 


1.8718 


7.06 


1.9544 


7.62 


2.0308 


5.39 


1.6845 


5.95 


1.7834 


6.51 


1.8733 


7.07 


1.9559 


7.63 


2.0321 


5.40 


1.6864 


5.96 


1.7851 


6.52 


1.8749 


7.08 


1.9573 


7.64 


2.0334 


5.41 


1 . 6882 


5.97 


1.7867 


6.53 


1.8764 


7.09 


1.9587 


7.65 


2.0347 


5.42 


1.6901 


5.98 


1.7884 


6.54 


1.8779 


7.10 


1.9601 


7.66 


2.0360 


5.43 


1.6919 


5.99 


1.7901 


6.55 


1.8795 


7.11 


1.9615 


7.67 


2.0373 


5.44 


1.6938 


6.00 


1.7918 


6.56 


1.8810 


7.12 


1.9629 


7.68 


2.0386 


5.45 


1.6956 


6.01. 


1.7934 


6.57 


1.8825 


7.13 


1.9643 


7.69 


2.0399 


5.46 


1 . 6974 


6.02 


1.7951 


6.58 


1.8840 


7.14 


1.9657 


7.70 


2.0412 


5.47 


1.6993 


6.03 


1.7967 


6.59 


1.8856 


7.15 


1.9671 


7.71 


2.0425 


5.48 


1.7011 


6.04 


1.7984 


6.60 


1.8871 


7.16 


1.9685 


7.72 


2.0438 


5.49 


1.7029 


6.05 


1.8001 


6.61 


1.8886 


7.17 


1.9699 


7.73 


2.0451 


5.50 


1.7047 


6.06 


1.8017 


6.62 


1.8901 


7.18 


1.9713 


7.74 


2.0464 


5.51 


1.7066 


6.07 


1.8034 


6.63 


1.8916 


7.19 


1.9727 


7.75 


2.0477 


5.52 


1.7084 


6.08 


1.8050 


6.64 


1.8931 


7.20 


1.9741 


7.76 


2.0490 


5.53 


1.7102 


6.09 


1.8066 


6.65 


1.8946 


7.21 


1.9754 


7.77 


2.0503 


5.54 


1.7120 


6.10 


1.8083 


6.66 


1.8961 


7.22 


1.9769 


7.78 


2.0516 


5.55 


1.7138 


6.11 


1.8099 


6.67 


1.8976 


7.23 


1.9782 


7.79 


2.0528 


5.56 


1.7156 


6.12 


1.8116 


6.68 


1.8991 


7.24 


1.9796 


7.80 


2.0541 


5.57 


1.7174 


6.13 


1.8132 


6.69 


1.9006 


7.25 


1.9810 


7.81 


2.0554 


5.58 


1.7192 


6.14 


1.8148 


6.70 


1.9021 


7.26 


1.9824 


7.82 


2.0567 


5.59 


1.7210 


6.15 


1.8165 


6.71 


1.9036 


7.27 


1.9838 


7.83 


2.0580 


5.60 


1.7228 


6.16 


1.8181 


6.72 


1.9051 


7.28 


1.9851 


7.84 


2.0592 


5.61 


1.7246 


6.17 


1.8197 


6.73 


1.9066 


7.29 


1.9865 


7.85 


2.0605 


5.62 


1.7263 


6.18 


1.8213 


6.74 


1.9081 


7.30 


1.9879 


7.86 


2.0618 


5.63 


1.7281 


6.19 


1.8229 


6.75 


1.9095 


7.31 


1.9892 


7.87 


2.0631 


5.64 


1.7299 


6.20 


1.8245 


6.76 


1.9110 


7.32 


1.9906 


7.88 


2.0643 


5.65 


1.7317 


6.21 


1.8262 


6.77 


1.9125 


7.33 


1.9920 


7.89 


2.0656 


5. -66 


1.7334 


6.22 


1.8278 


6.78 


1.9140 


7.34 


1.9933 


7.90 


2.0669 


5.67 


1.7352 


6.23 


1.8294 


6.79 


1.9155 


7.35 


1.9947 


7.91 


2.0681 


5.68 


1.7370 


6.24 


1.8310 


6.80 


1.9169 


7.36 


1.9961 


7.92 


2.0694 


5.69 


1.7387 


6.25 


1.8326 


6.81 


1.9184 


7.37 


1.9974 


7.93 


2.0707 


5.70 


1.7405 


6.26 


1.8342 


6.82 


1.9199 


7.38 


1.9988 


7.94 


2.0719 


5.71 


1.7422 


6.27 


1.8358 


6.83 


1.9213 


7.39 


2.0001 


7.95 


2.0732 


5.72 


1 . 7440 


6.28 


1.8374 


6.84 


1.9228 


7.40 


2.0015 


7.96 


2.0744 


5.73 


1.7457 


6.29 


1.8390 


6.85 


1.9242 


7.41 


2.0028 


7.97 


2.0757 


5.74 


1.7475 


6.30 


1.8405 


6.86 


1.9257 


7.42 


2.0041 


7.98 


2.0769 


5.75 


1.7492 


6.31 


1.8421 


6.87 


1.9272 


7.43 


2.0055 


7.99 


2.0782 


5.76 


1.7509 


6.32 


1.8437 


6.88 


1.9286 


7.44 


2.0069 


8.00 


2.0794 


5.77 


1.7527 


6.33 


1.8453 


6.89 


1.9301 


7.45 


2.0082 


8.01 


2.0807 


5.78 


1.7544 


6.34 


1 . 8469 


6.90 


1.9315 


7.46 


2.0096 


8.02 


2.0819 


5.79 


1.7561 


6.35 


1.8485 


6.91 


1.9330 


7 . 47 


2.0108 


8.03 


2.0832 


5.80 


1.7579 


6.36 


1.8500 


6.92 


1.9344 


7.48 


2.0122 


8.04 


2.0844 


5.81 


1.7596 


6.37 


1.8516 


6.93 


1.9359 


7.49 


2.0136 


8.05 


2.0857 



APPENDIX 
HYPERBOLIC LOGARITHMS 



781 



No. 


Log. 


No. 


Log. 


No. 


Log. 


No. 


Log. 


No. 


Log. 


8.06 


' 2.0869 


8.58 


2.1494 


9.24 


2.2235 


9.90 


2.2925 


19.00 


2.9444 


8.07 


2.0882 


8.60 


2.1518 


9.26 


2.2257 


9.92 


2.2946 


19.50 


2.9703 


8.08 


2.0894 


8.62 


2.1541 


9.28 


2.2279 


9.94 


2.2966 


20.00 


2.9957 


8.09 


2.0906 


8.64 


2.1564 


9.30 


2.2300 


9.96 


2.2986 


21 


3.0445 


8.10 


2.0919 


8.66 


2.1587 


9.32 


2.2322 


9.98 


2.3006 


22 


3.0910 


8.11 


2.0931 


8.68 


2.1610 


9.34 


2.2343 


10.00 


2.3026 


23 


3.1355 


8.12 


2.0943 


8.70 


2.1633 


9.36 


2.2364 


10.25 


2.3279 


24 


3.1781 


8.13 


2.0956 


8.72 


2.1656 


9.38 


2.2386 


10.50 


2.3513 


25 


3.2189 


8.14 


2.0968 


8.74 


2.1679 


9.40 


2.2407 


10.75 


2.3749 


26 


3.2581 


8.15 


2.0980 


8.76 


2.1702 


9.42 


2.2428 


11.00 


2.3979 


27 


3.2958 


8.16 


2.0992 


8.78 


2.1725 


9.44 


2.2450 


11.25 


2.4201 


28 


3.3322 


8.17 


2.1005 


8.80 


2.1748 


9.46 


2.2471 


11.50 


' 2.4430 


29 


3.3673 


8.18 


2.1017 


8.82 


2.1770 


9.48 


2.2492 


11.75 


2.4636 


30 


3.4012 


8.19 


2.1029 


8.84 


2.1793 


9.50 


2.2513 


12.00 


2.4849 


31 


3.4340 


8.20 


: 2.1041 


8.86 


2.1815 


9.52 


2.2534 


12.25 


2.5052 


32 


3.4657 


8.22 


2.1066 


8.88 


2.1838 


9.54 


2.2555 


12.50 


2.5262 


33 


3.4965 


8.24 


2.1090 


8.90 


2.1864 


9.56 


2.2576 


12.75 


2.5455 


34 


3.5263 


8.26 


2.1114 


8.92 


2.1883 


9.58 


2.2597 


13.00 


2.5649 


35 


3.5553 


8.28 


2.1138 


8.94 


2.1905 


9.60 


2.2618 


13.25 


2.5840 


36 


3.5835 


8.30 


2.1163 


8.96 


2.1928 


9.62 


2.2638 


13.50 


2.6027 


37 


3.6109 


8.32 


2.1187 


8.98 


2.1950 


9.64 


2.2659 


13.75 


2.6211 


38 


3.6376 


8.34 


2.1211 


9.00 


2.1972 


9.66 


2.2680 


14.00 


2.6391 


39 


3.6636 


8.36 


2.1235 


9.02 


2.1994 


9.68 


2.2701 


14.25 


2.6567 


40 


3.6889 


8.38 


2.1258 


9.04 


2.2017 


9.70 


2.2721 


14.50 


2.6740 


41 


3.7136 


8.40 


2.1282 


9.06 


2.2039 


9.72 


2.2742 


14.75 


2.6913 


42 


3.7377 


8.42 


2.1306 


9.08 


2.2061 


9.74 


2.2762 


15.00 


2.7081 


43 


3.7612 


8.44 


2.1330 


9.10 


2.2083 


9.76 


2.2783 


15.50 


2.7408 


44 


3.7842 


8.46 


2.1353 


9.12 


2.2105 


9.78 


2.2803 


16.00 


2.7726 


45 


3.8067 


8.48 


2.1377 


9.14 


2.2127 


9.80 


2.2824 


16.50 


2.8034 


46 


3.8286 


8.50 


2.1401 


9.16 


2.2148 


9.82 


2.2844 


17.00 


2.8332 


47 


3.8501 


8.52 


2.1424 


9.18 


2.2170 


9.84 


2.2865 


17.50 


2.8621 


48 


3.8712 


8.54 


2.1448 


9.20 


2.2192 


9.86 


2.2885 


18.00 


2.8904 


49 


3.8918 


8.56 


2.1471 


9.22 


2.2214 


9.88 


2.2905 


18.50 


2.9173 


50 


3.9120 



APPENDIX III. 

Certain illustrations presenting historical interest and incorporating 
features of design discussed in the body of the text will be of value to 
students in this field. 




Fic 259A -Watt wagon boiler, showing automatic float water feed, automatic damper 
reguTator by pressure and hopper-fed automatic mechanical stoker. 
° 782 



APPENDIX 



783 




784 



APPENDIX 




APPENDIX 



785 




Bradley ^ Poates, Engi-'s. N. T, 

Fig. 359A. — Back-acting Hudson River paddle wheel tow-boat engine. S.S. Belle. 



786 



APPENDIX 







o 
o 

a 
'So 

< 



APPENDIX 



787 




Fig. 383A.— Direct vertical pumping engine by Holly Mfg. Co. 



788 



APPENDIX 




APPENDIX 



789 





I 
O 

O 

6 

O 

I 



790 



APPENDIX 





Fig. 402.— Brooklyn Wat«r W 




Dl:l|>er 
Uii of 



Of Cylinder ...90' 

Stroke of Piston 10' 

of Pumps 2 

Working Barrel 36' 

AuxiUiary Barrel &1" 

Pu[lStroke 10 

]!^alves of the double-beat 
k^'... 



Dc ^-acting Air Pump 

DiiJtierof AirPump 3' 

1(6131 of Stroke 5' 

0eiliof centre of Beam above 

^i, Cornish Pumping Engine. 



LU.TUERS & CO.>ENGa'8, Nj^fiT 

level of Floor- 26'? 

Length of Beam between end 
centres 30' 

Depth of Beam in middle 7'a* 

Average thickness of Web 0'6" 

Diameter of Air Chamber 6' 6i' 

Height of A ir Chamber SS'i' 

„" " " " above 
Floor 1310' 

Total weight of Engine, Boilers 
and Appurtenances 440 Tons 



I 



APPENDJX 



791 




792 



APPENDIX 





= o 






APPENDIX 



793 




794 



APPENDIX 




APPENDIX 



795 




o 



^ 



796 



APPENDIX 




APPENDIX 



79- 




798 



APPENDIX 




Fig. 666 a. — Surface condenser packings and joints. 



APPENDIX 



799 






Fig. 669A.— Colt disk engine. 




(800) Fiu. 697^ . — Babcock and Wilcox cut-off valve tlirowu by steam 



INDEX 



PAGE 

A frame of vertical engine 406, 417, 568 

Absorption dynamometer 763 

Accelerations in engine mechanism 393 

Accidents in engine-room 757 

Acid test for oils 745 

Action of curving rolls 32 

steam in compound engines 471 

Adamson ring for flues : 96 

Advancing stem valve 352 

Air cooling of injection-water 728 

compressor, back~a,cting, Rand's 384 

pump and foot- valve 719, 731 

riveting machine 46 

space in grates 174 

valves 591, 666 

Alarm for low water 268 

Alberger condenser 722, 727, 730 

Alinement of foundation-template 555 

outer pillow-block or outboard bearing 558 

Allan link-motion 688 

Allen link-motion 691 

resistance governor 712 

sectional boiler 153 

valve 658 

Allis-Chalmers compoimd steam turl:)ine 524 

Almy boiler " 157 

American mechanical stoker 313 

Analysis of a power plant 4, 7, 8 

Angle-engine 414 

valve 350 

Angstrom valve-gear 690 

Annealing of steel boiler-plate 42 

Apparatus for drawing motion-curves 791 

Argand principle in gas firing 227 

Armington & Sims piston- valve 664 

Arrangement of a power plant 769 

rings in boiler-shells 34 

rivets in a joint 51 

Artificial draft 202 

Asbestos packings 588 

Ash handling machinery 308 

801 



802 INDEX 

PAGE 

Ash-pit in boiler-settings 186 

doors in boiler-settings 220 

Attached air-pump 241, 734 

feed pump 241 

Automatic cut-off engine 457 

damper-regulator 198 

injectors 259 

stokers 309 

water-feeding apparatus 269 

Auxihary engine for valve-motion of pumps 246 

Babcock & Wilcox engine-governor 706 

engine with steam-thrown valve 800 

feed-water filter '. 290 

mechanical stoker 310 

sectional boiler 144 

Back-acting engine 382 

Back connection 194 

pressure valves 367 

Bacon's trunk-engine 784 

Bagasse furnace 235 

Balanced engine, Durfee's 583 

Wells' 548 

governor 705 

slide-valves 662 

Balancing of engines 545 

Baldwin locomotive fire-box Ill 

Baldwinsville rotary pump 500 

Ball Engine Co. tandem compound 479 

Banking fires of boilers 280 

Baragwanath feed-water heater 322 

Barometric condenser 737 

Bates-Corliss cylinder and valve-gear 634 

engine bearing 616 

engine cross-head 592 

tandem-engine foundation 552 

Bay City Iron Works, upright boiler . ; 124 

Beam compound engine 478 

Beam-engine 416 

Bearings, lubrication of 744 

Bed or frame of a vertical engine 568 

Bed-plate of a horizontal engine 544 

Belle, engine of 785 

Bellerophon, engine of 783 

Belpaire fire-box 112 

Bent-tube sectional boilers 151 

Bernouilli theorem in Venturi meter ; 333 

Berryman feed-water heater 317 

Blast-furnace boiler • 131, 133 

BUsters in boiler-plate 48 



INDEX 803 

PAGE 

Blowing-engine, back-acting » 382 

Blow-off pipe and valve . . .* = 252 

Bogie cross-head guides . . . ...,,.. 593 

Boiler accessory apparatus ...,.,. 240 

energy stored in 20 

explosions 298 

forms 19 

fronts 220 

function of 19 

furnace o . . 165 

heads , 35 

horse-power, A.S.M.E. standard 15 

inspection 298 

locomotive 109 

management 279 

manufacture , 19 

marine 103 

materials 19, 30 

of steamer Bergen 108 

Orange 110 

patches 297 

plant auxiliaries 306 

plate, curving of , 32 

punching-press 40 

steel 30 

testing of 30 

thickness of 28 

wrought-iron 47 

repairs 296 

rupture 300 

scale 282 

sectional 130 

setting 165, 215 

shapes of 19 

shell with few joints 32 

shells, joints in 37 

specifications for material , 30 

test for efficiency 760 

tubes 87 

Boilers, corrosion of 293 

classification of 83 

deterioration of 292 

grooving of 295 

hanging of 208 

internally fired 100 

overheating of 292 

testing 298 

unequal contraction of 292 

expansion of 292 

wear and tear of 292 



804 INDEX 

PAGE 

Bolts for engine-foundation 554 

Boring of cylinder .* 573 

Boston pumping-engine fly-wheel 624 

Bourdon gage for boiler 273 

Bowling rings for flues 96 

Box-piston 578 

Braces, see Stays. 

Brake-horse-poY/er , 3 

Brasses of connecting-rod 601 

Breeches boiler 103 

Bridge-wall 187 

Brown valve-gear 690 

Buckeye engine bed-plate 562 

engine valve 659 

Buck-stays 217 

Built-up crank 610 

Bull Cornish pumping-engine 429 

ring 578 

Bump-joint for flues 95 

Bursting pressure for boilers 26, 47 

Bushing for stub end 604 

Buss-governor 706 

Butt-joint 50 

B valve , 640 

By-pass valve for compound engines 755 

Cahall water-tube boiler , 140 

Caldwell mechanical shovel 314 

Calibration of steam-gage 274 

Calking of boiler-seams 70 

Calorific power of a fuel 17 

Calorimeter test for quahty of steam 330, 761 

Cam and release valve-gear 670 

riveting-machine . 46 

Card from indicator 442 

Care and management of boilers 279 

engines 753 

Case oscillating engine 379 

Cast-iron crank 608 

for boiler material 47 

grates 174 

packing-rings 581 

Cataract of Cornish engine 431 

Center-crank engine 438 

Centrifugal circulating pump 735 

governors 699 

separator for steam-pipe 358 

Chain grate 179, 310 

Chain riveting 55 

Challenge reversible rotary engine 501 



INDEX 805 

PAGE 

Charcoal-iron in boilers 47 

Check- valves on feed-pipes 250 

Chimney heights of 173 

Chimneys 165, 198 

Circulating pump ' 735 

Circulation process 23 

Classes of sectional boilers 137 

Classification of boilers by type 84 

engines by use of steam 445 

governors 699 

Clayton air-compressor . . . . ; 245 

Cleaning fires of boilers 279 

the heating surface of boilers 281 

Closed heater 320 

stoke-hole 202 

stub end 602 

tube sectional boiler 153 

Coal, calorific power of 166 

handling machinery 307 

per horsepower per hour 15 

square foot of grate 199 

Coil-boiler 155 

Cold-water test of boilers 299 

well 728 

Cole superheater 327 

Collar-bound bearing 614 

Colt or West disk-engine 800 

Column-pipe for water-gage 261 

Combination horizontal and vertical engine 414 

Combustion, air for 26 

chamber 190 

computations in 26 

external 2 

indicators 330 

in locomotive boilers 112 

internal 2 

per square foot of grate 16 

Combustion rate 16 

Comparative cost of turbine and engines 539 

Compensators in non-fly wheel pumps 478 

Composite band-wheels 626 

Compound engines 465, 467 

locomotives 485 

rotary engine 504 

turbines 514 

Compounding above atmosphere 490 

without condensation 490 

Compressed air for transmitting power 765 

Compression as a method of governing 396, 452, 50, 642 

in the steam cylinder 2396 



806 INDEX 

PAGE 

Concave calking 70 

Concentrated or subdivided steam-power 764 

Concrete foundations 553 

Condenser of a condensing engine 717 

Condensers for steam turbines 743 

Condensing engines . 460 

Conditions for use of tubular boilers 92 

Conical pendulum-governor 701 

Connecting-rod , 599 

Connections of the governor to control the engine 716 

Construction of a power house 768 

engine-foundations 550 

riveted joint 40 

Continuous-expansion engines . 468 

Control of energy in steam-engines 446, 618, 699 

Convection process 23 

CooHng effect of water on hot plate . , 304 

towers 728 

Copper as boiler material , 47-87 

steam-pipe 340 

Corliss bed-plate '. 565 

pumping-engine, Pawtucket 425 

valve-gears 675 

Corliss steam-jacket joint 576 

upright boiler 125 

Cornish boiler *. . . . 102 

Cornish engine 429 

cataract 431 

Corrosion of boilers 293 

Corrosion of steel boiler-plates 105 

Corrugated flues and furnaces 119 

furnace for locomotives 116 

pipe for expansion, Wainwright's 347 

Cost of a horsepower . 18 

steam turbine 538 

Counterbore in the cylinder 574 

Counterweighted crank. . 608 

Coxe chain-grate 180 

Cracking of steam boiler-plate 31, 56 

Craig pump-condenser 799 

Cranked axle 609 

Crank end of cylinder 374 

kinematics of 376 

pin 608 

pin oiler 749 

shaft 607 

Cross-compound engine 484 

head 595 

head pin 598 

Crown-bars , '. ' 64-112 



i 



INDEX 807 

PAGE 

Crown-sheet stays 64-112 

Cup leather packing 580 

Curtis steam turbine 525 

Curved-tube sectional boilers 149 

Curving boiler-plate 32 

Cushioning in c. steam-cylinder 396 

Cut-off defined 453 

engines 446 

governors 695, 710 

Cylinder boiler 132 

casting 569 

cocks 574 

cover 570 

in multiple-expansion engines, arrangement of 487 

jacket 575 

of Worthington-Corliss engine 481 

volume 10 

Dake square-piston engine 800 

Damper in chimney-flue 196 

regulator 196 

D'Arcy's coefficients for flow in pipes 338 

Dashpots of Corliss valve-gear 679 

Dead-centers of engine 386 

plate of furnace 184 

Dean beam pumping-engine 423 

De Laval steam turbine 511 

Density of chimney gases 169 

Design of a riveted joint * 50 

slide-valve 647 

Detached feed-pump 243 

Deterioration of boilers 292 

Diaf ram steam gage 272 

Diagonal engines, see Inclined. 

Diagram of compound engine 492 

condensing and non-condensing engines 462 

effort in a cut-off engine 446 

throttling-engine 458 

expansive working 446 

non-expansive working 458 

showing loop 449 

triple engine 494 

Woolf compound engine 492 

Differential governors 700 

Dilution of chimney gases 174 

Direct-acting engines 416 

pump for boiler-feed 245 

vertical engine 408 

Disengagement area 24, 72 

governors 700 




808 INDEX 

PAGE 

Disk-crank 608 

Disk-engine 800 

Distribution of power by gas, electricity, or air 765 

Domes for boilers 73 

Double- and single-acting engines 429 

connecting-rod 605 

Cornish boiler 102 

crank '. 608 

ported valve 659 

riveted joint. . . .T 50 

tube-injector 258 

Down-draft furnace 210 

Dow steam turbine 514 

Draft, artificial, forced and mechanical. . ., 315 

Drainage of steam-pipe 354 

Drift-pin 56 

Drilling of boiler-plate for rivet-holes 41 

Drip-connections 369 

Dry air-pump 732 

Dry pipe in boilers 75 

Dudgeon's tube-expander 88 

Dumping-grates 176 

Dunbar packing , 584 

spray boiler 160 

Durfee's piston-packing 583 

Dutch oven furnace ". . 139-212 

D valve 640 

Dynamic equivalent of a heat-unit 12 

Dynamic stresses in mechanism 390 

Dynamometers 763 

Dynamometric governors 713 

Eccentric 614 

fittings for steam-pipe 354 

is a crank 637 

rod 615 

strap 616 

Economical point of cut-off 453 

Economizers 316 

Economy of heating feed-water 315 

Edge planing of boiler-plate 70 

Edmiston oil-filter ^ 365 

Edwarde's air-pump 733 

Efficiency defined 445 

of a riveted joint 49 

the injector 256 

Egg-ended boiler 28 

Ejector condenser with pump 721 

Electrical distribution of power 765 

Electromagnetic governors 712 




INDEX 809 

PAGE 

Elephant boiler 132 

Energy resident in hot water 21, 301 

sources of 2 

stored in a boiler 20, 302, 305 

Engine constant in horse power formula 11 

foundations and bed-plates 544 

lubrication 744 

management 753 

mechanism, dynamics of 371 

testing 762 

Equilibrium-valve of Cornish engine 431 

Ericsson vibrating engine 789 

Evaporation by American coals 17 

per square foot of heating-surface ^. ..... . 84 

process. 21 

Exhaust clearance 643 

heads 366 

injectors 260 

lap 643 

Exhaust pipe 362 

steam ejector condenser 739 

heaters 317 

turbines 529 

Expanding of tubes -, ". 88 

Expansion of boilers 219, 292 

joints for steam-pipe 345 

Expansion valve-gear 640 

Expansive and non-expansive working of engines 446 

Explosions of boilers 298 

Extension-fronts in boiler settings 221 

External combustion 2 

External fire-box for boilers 84, 209 

Externally-fired boilers 84 

Extractors for oil 363 

Failure of a riveted joint 56 

Fall River Steamboat Co. inclined compound engine 413 

False seat for valve 698 

Farcot governor 705 

Feathering paddle-wheels . 411, 413 

Feed-pipe 249 

pump of condensing engine 741 

pumps for boilers 240 

water, filtration of 291 

heating 315 

introduction of 250 

purification of , 290 

valves 249 

Ferry-boat engine without walking-beam 411 

Fibrous packings 587 



810 INDEX 

PAGE 

Field tubes 24, 128, 152 

Filters for oil 365, 752 

Filtration of feed-water 291 

Fink link-motion 692 

Fire-box steel 30 

Fire-brick arch for locomotive-boilers 100, 112 

doors in boiler-settings 222 

engine boiler 127 

rotary 502 

protection of a power plant 769 

Fire-tube boilers 84 

proportions 91 

Fire-tubes 25 

Firing of boilers 184, 227, 279 

Fishkill Landing Corliss engine 795 

Fittings for pipe 340 

Fixed pressure-plate system of Atlas engine 666 

Flaming coals, boilers for 97—112 

Flange joint for pipe 341 

Flange steel 30 

Flanging of heads 35 

Flash and semi-flash boilers 155 

Flexible expansion- joint 345 

plate balancing system 669 

stay bolts, Tate's 66 

Flexure of butt-joint ' 50 

lap-joint 39, 292 

Flinging stresses of connecting-rod 400 

Float water-gages 266 

Floors of a power plant 770 

Flue-boiler 92 

doors in boiler-settings 225 

gases, quality of " 761 

heaters 316 

Flue brushes and scrapers 280 

Flue to chimney 195 

Flush fronts in boiler-settings 221 

Fly-ball or conical pendulum governor 701 

Fly-band-wheels 626 

Fly-wheel 617 

pump for boiler feed 244 

Footings for engine-foundations 552 

Foot-valve of air-pump 731 

Forced draft 202, 315 

Fore-and-aft-compound engine , 483 

Forged crank 608 

Forked connecting-rod 605 

Formulae for flues, U. S 97 

Forward-running engine 389 

Foster superheater , , ,..,... 326 



INDEX 811 

PAGE 

Foundation-bolts , 554 

Foundations for engines 544 

Foundation template 555 

Free expansion in compound engine 473, 492 

French boiler 132 

Friction in pipes 338 

of slide-valves 663 

Fritz piston-packing 584 

Front connection 195 

Fuel oil under boilers 227 

source of motor energy 2 

Fuels, calorific power of 166 

FuU.fronts in boiler-setting 221 

Fuller's marine-engine governor 716 

Function of the power plant 1 

boiler 19 

Furnace in boiler-settings 165, 184 

Fusible plugs 268 

Gab-hooks 683 

Gage-cocks 266 

Gages, steam, calibration of 274 

recording 274 

water 260 

Galloway tubes in Lancashire boiler 103 

Gallows-frame of beam-engines 417 

Gallows frames for boilers 225 

Gang-drill 41 

Gang or multiple punch , 41 

Gardner spring-governor 707 

Gas as fuel 227 

Gaskets for steam-pipe 342 

Gaskill or Holly inclined pumping-engine , . 412 

Gaskill pumping-engine 421 

Geared fly-wheels 627 

Gib and key for connecting-rod 601 

Gibs for crosshead 596 

Giddings engine-valve 669 

Girder bed-plate section 566 

Gland in stuffing-box , 586 

Glass water-gage 261 

Gooch link-motion 688 

Gonzenbach two-valve gear 693 

Gordon & Maxwell cataract-cylinder 432 

Governing for steam-engines 455, 618, 699 

Governing in steam-turbines 519, 529 

Grading of steam-pipe 354 

Graphite as a lubricant 748 

Grate and heating-surface , 17 

Grate-bars in boiler-settings 174 



812 INDEX 

PAGE 

Grates inclined and horizontal ., 181 

Grate surface for a combustion rate 16 

Gravity as motor force 2 

Gravity condenser 737 

separator for steam-pipe 357 

Grease-cups • 751 

Green economizer 316 

Greene valve-gear 676 

Gridiron slide-valve 659 

Grooving of boilers 295 

Guides for slides 592 

Gusset-stays 65 

Hackworth valve-gear , 690 

Haight-joint for fly-wheel rims 625 

Half-blind hole 24 

Half-fronts in boiler-settings 221 

Hammer test of boilers 299 

Hand-holes 70 

riveting 43 

Hanging of boilers 218 

steam-pipe 347 

Harrison boiler 138 

Hawley down-draft furnace 210 

Head end of cylinder 374 

Heads of boilers *. . . . 35 

Heat balance 236 

Heat, transfer of 14 

unit, dynamic equivalent of 12 

Heating effect of steel plate 304 

Heating of bearings 751, 758 

Heating-surface and grate-surface 14, 17 

Heine sectional boiler 142 

Herreshoff water-tube boiler 160 

Heusinger von Waldegg gear 691 

High-speed engines 426 

Historical summary 771 

Hollow bridge-wall 192 

piston-valve 664 

Hoppes feed- water heater - 289 

Horizontal engine 405 

grates 181 

sectional boiler 141 

separator for steam-pipe 358 

tubular boiler 84 

vertical engine 414 

Homblower compound engine 478, 482 

Horsepower, brake 1 

cost of 18 

defined 4 



INDEX 813 

PAGE 

Horsepower indicated 3 

in metric units 4 

nominal 4 - 

of a boiler 15 

of a boiler A.S.M.E. standard 15 

of a cylinder- 10 

of a piston-motor 10 

of the resistance • 3 

Hot-water test of boilers 299 

Hot-well 740 

Houston, Stanwood & Gamble 18-flue boiler 93 

Hungarian street-railway power-plant engine 408 

Hunting of engine-governors 704 

Huntoon resistance governor 712 

Hunt stub end 791 

Z-crank engine 800 

Hydraulic reversing-gear 694 

riveting-machine 45 

Hydrokineter Weirs 107 

Hydrostatic test of boilers 299 

Ide breaking-cap 575 

engine cross-head 596 

Inclined-cylinder beam-engine 420 

Inclined engine 409 

grates 181 

Incrustation or scale in boilers 282 

Independent air-pump 734 

Independent feed-pump 241 

Indicated horse-power 3 

Indicator 442 

Induced draft 204, 315 

Inertia forces in mechanism 393 

Inertia-governors 710 

Injection defined 718 

weight of 719 

Injector 253 

Injector condenser 737 

I-section for connecting-rod 400, 600 

Inside lap 642 

Inspection of boilers 298 

Inspirator 258 

Intercepting- valves in compound locomotive 474, 485 

Intermediate cylinder defined 469 

Internal combustion 2 

Internal condensation and re-evaporation defined 322, 449, 470, 577 

Internally-fired boiler defined 100 

International boiler 151 

Introduction of feed-water 250 




814 INDEX 

PAGE 

Inverted vertical engine 408 

Isochronous governing 695 

Jet condenser 72q 

Joint of bed-plate and foundation 557 

Joints in boiler-shells 37 

of surface-condenser tubes 726 

Joints in steam-pipe 340 

Jones mechanical stoker 313 

Joy valve-gear 688 

Junk-ring 577 

Kennedy spiral punch for boiler-plate 41 

Kent chimney formula 171 

Kerr steam turbine 515 

Key and cotter for connecting-rod 600 

Keys for crank 608 

Kilowatt defined ; 4 

Knock or pound in engine-bearings 758 

Klinger water-glass-gage 265 

La France rotary engine 500 

Lagging the cylinder 575 

Laketon tandem oil-pumping engine 481 

Lamination in boiler-plate 48, 292 

Lancashire boiler 102 

Lane & Bodley connecting-rod 602 

cross-heads 595 

outboard bearing 559 

Lane steam-gage 273 

Lap in slide-valve 640 

Lap-joint with cover-plate 54 

Lap-riveted joints .' 50 

Law metallic packing 590 

Lead in the slide-valve 644 

varies in Stephenson link-motion 687 

Leakage-grooves in pistons 580 

Leavitt beam-engine (Lawrence) 420 

Leavitt, Calumet and Hecla, butt-joint 54 

steam jacket-joint 576 

Left-hand engines , 436 

Length of engine 376 

Lever riveting-machine , 46 

safety-valve 277 

Lidgerwood reversible rotary engine 501 

Lifting valves 628 

Lime catcher 289 

Limitations of the single slide-valve 653 

Link-motion for riding cut-off valves 691 

of Stephenson or Howe and others 685 

Liquid fuel burners, furnaces 230 



INDEX 815 

PAGE 

Loaded governors 704 

Locating the bed-plate on the foundation 556 

Location of a power plant 766 

Locomotive boiler 109 

crank 609 

derivatives of 119 

fire-box, Woods 118 

proportions 119 

reverse gear of P. R. R 685, 692 

Long cylinder-boilers hanging of ... 132 

Loss in blowing-off 253 

Low-pressure steam turbines 529 

Low-speed engines 427 

Low-water alarm 268 

Lubrication of the engines 742 

Lugs for hanging boilers ; 218 

McEwen double piston-valve 573 

McNaughted engines 478 

Machine-riveting 43 

Magazine feeding-apparatus 269 

Main bearing 612 

Malleableized iron in boilers 47 

Management of boilers 279 

engines 753 

Manholes 66 

Manning boiler 123 

Marden down-draft furnace 211 

Marine boiler 103 

connecting-rod 604 

crank-shaft 611 

cylinder relief-valve 575 

engine-governors 714 

steam turbines 530 

triple open-frame engine 381 

Marshall valve-gear 690 

Martin boiler 107 

Mass of engine foundation 545 

Materials for boilers 19, 30 

Mattes connecting-rod 604 

Mean pressure in expansion 10, 465-495 

Mechanical draft 202 

grates 179 

stokers 181, 309 

Mechanism of compound engine 475 

engine , ' 376 

Mesh separators 77 

Metallic packings 589 

Meters, water 332 

Meyer riding cut-off 655, 697 



816 INDEX 

PAGE 

Milwaukee Allis inverted vertical pumping-engine 410 

Mineral matter in feed-water 283 

Mississippi gage-cock 267 

Modifications of locomotive-boiler 116 

Monadnock monitor engine 788 

Monitor half -beam engine 788 

Morrison furnace flue 106 

Morton ejector condenser 739 

Mosher's sectional boiler 152 

Motion-curves for slide-valves 792 

Motor energy, sources of 2 

Mouthpiece of boiler-furnace 222 

for manholes 68 

Mud-drum 79 

Multicellular steam turbine 514 

Multiple-expansion engines . . . 465, 467 

rivet butt-joint 54 

Multiported valve seat 659 

Multitubular boiler 84 

Murdoch long valves 658 

Myers furnace 235 

Napier connecting-rod 604 

Nasmyth test for gum in oils 645 

Nominal horse-power -. . . . 4 

Non-advancing stem- valve 352 

Non-condensing engines 460 

Non-conducting coverings for steam-pipe 360 

Non-expansive working of engines , 444 

Non-fly-wheel pump ■. 245 

Nozzles for manholes 68 



Oil as fuel 227 

Oil-cup lubricator 747 

Oil-extractors and separators 363 

Oil-filters 364, 752 

Open-frame engine 408 

Open heater 320 

Open-stub end • 602 

Operation of steam turbines 540 

Orsat flue gas apparatus 330-761 

Orsat gas-analysis apparatus 761 

Oscillating engine 378 

paddle-engine 380 

Outboard bearing, alinement of 558 

Output of a power plant » 3 

Outside lap 640 

Overheating of boilers 292 

Overload capacity of turbines 519 



INDEX 817 

PAGE 

Packings for piston-rods 587 

Paddle-wheel engine of L. B. &. C. Ry 411 

Parabolic governor 704 

Parallel motions 599 

Parsons steam turbine 519 

Patches on boilers 297 

Peclet's theory of chimney draft 170 

Pendulum engine 789 

Pennsylvania R. R. locomotive link-motion 685, 692 

Perforated dry pipe 76 

Performance of steam turbines 541 

Phosphorus in boiler plate 31 

Pickering's spring governor 707 

Pierce rotary boiler 129 

Pin-drill for tube-sheets . , 87 

Pipe and fittings boilers 155 

Pipe fittings 340 

Piping of pressure ' 335 

Piston motor, horse power of 10 

Piston-packings 578 

rings 581 

rod 584 

speed 428 

structure of 576 

valve 663 

Pitman in beam-engines 416 

Pitting of boilers 295 

Plain cylinder-boiler 130 

slide-valve working full stroke 635 

Plate piston 583 

Plug fusible 268 

Pneumatic riveter 46 

Polar diagram for slide-valves 647 

Polonceau link-motion 693 

Poppet-valves 628, 670 

Pop safety-valve 277 

Porter- Allen pressure-plate system 667 

two- valve gear 656 

Porter engine bed-plate 562 

analysis of 4 

function of 1 

Porter loaded governor 704 

Porter steeple compound engine 477 

Pounds of air per pound of coal 26 

coal per square foot of grate 172 

water per horse-power per hour 13 

pound of coal 16 

Power house, construction of 768 

plant, arrangement of 769 

fire protection of 770 



818 INDEX 

PAGE 

Power plant, floors of 770 

location of 766 

Power reversing-gears 693 

Precautions in oil firing 231 

Preheating feed-water , . . 315 

Pressure-plate to balance slide-valve 665 

Prevention of boiler-scale 287 

Prevention of smoke 208 

Previous purification of feed-water 290 

Priming of boilers 72, 285 

Proportions of compound-engine cylinders 470 

Prosser tube-expander 88 

Pulverized fuel for firing ! 227-234 

Pump condensers : 721, 739, 799 

governor 710 

lubricators 746 

valves 249 

Pumping-engine, Corliss 425 

Dean 423 

direct vertical type 410 

Gaskill horizontal beam 421 

Leavitt, Lawrence 420 

Punching and drilling compared 40 

Punch and die for boiler-plate 41 

Quadruple-expansion engines 485 

Quadruple riveted-joint 56 

Quantitative basis of the power plant 10 

Quarter-boxes 612 

Quartering cranks. . 399 

Radial valve-gear 688 

Ransom gravity or siphon condenser , 738 

Rateau steam turbnie 516 

Rate of combustion 16 

Rates of combustion per square foot of grate 16 

Ratio of expansion 453 

Ratio of grate-surface to heating-surface 17 

Reaction steam turbine 513 

Reaction in boiler-explosions 303 

Reaming of holes for rivets 43 

Receiver compound engine 484, 490 

Reciprocating steam-engine, parts of 372 

Recording-gauge 27S 

Rectangular marine boiler 107 

Reduced compound-engine diagram 494 

Reducing valves 368 

Re-enforced domes for boilers 75 

Re-evaporation -defined 322, 449, 470, 577 

Regulation of boiler-fires 280 



INDEX 819 

PAGE 

Re-heater in compound locomotive 490 

Re-heaters for compound engines 490 

Releasing- valve gears 675 ' 

Relief-valve 275, 574 

Relief- valves in the cylinder 574 

Removal of boiler-scale 286 

Repairs to boilers 296 

Resistance governors 710 

Restarting injectors 259 

Retarders in boiler-tubes 90 

Reversing- valve gears 682 

Revolving valves 630 

Reynolds upright boiler 126 

Ribbed tubes for boilers 90 

Richardson locomotive balanced valve 590, 666 

Rider automatic cut-off with trapezoidal ports 698 

Riding cut-off 656, 697 

Riedler-Stumpf steam turbine 513 

Right-hand engine - 436 

Ringelmann's smoke chart 213 

Rites inertia shaft governor 710 

Rivet steel 30 

Riveted joint, design of 37, 49 

failure of 56 

strength of 50 

joints for boiler-shells 39 

Riveting of piston-rods 584 

Rocking grates 176 

valve cam 670 

Rocking valves 630 

Rockwood compound engine 469 

Roller bearings for valves 670 

Rolls for curving plate, Hilles & Jones 33 

Roney mechanical stoker 312 

Root sectional boiler 147 

Rotary steam-engine 497 

Running of engines 753 

Rupture of boilers 301 

Safety-plugs 268 

stops 713 

valve 275 

water-gage 261 

Sarco combustion indicator 331 

Sawdust fuel furnace 235 

Scale clogging feed-pipes 249 

in boilers 282 

Schutte exhaust steam-condenser 739 

Scotch marine boiler 103 

Seacock for marine-engine condenser 721 



820 INDEX 

PAGK 

Sectional boilers .- 134 

coverings for steam-pipe 360 

' Segmental fly-wheels 623 

Selection of type of boiler 96 

Sellers hydraulic riveting-machine 45 

steam riveting-machine , 44 

Semi-flash boilers 155 

Separator, mesh 77 

Separators for oil 363 

steam-pipe 354 

Serve-tubes for boilers 90 

Setting of non-expansive slide-valve 638 

valve by indicator 645 

sound : 645 

trammel 645 

Shaft-driven pump 242 

Shaft-bearing 612 

Shaft-governors 709 

Shaft of marine engine , 611 

Shaking forces in bed-plates and foundations 545 

Shaking-grates 176 

Shapes of boilers 32 

Shaping shell elements 35 

Shell boilers, externally fired 84 

internally fired 180 

Shims in alining engines 557 

Shortening steam-passages 657 

throw of a valve 658 

Shrinkage of pistons 586 

Shunt water meter 333 

Shut-downs in the engine room 757 

Sickles cut-off 675 

Side-by-side compound engine 483 

Side cam 671 

crank engine 438 

lever engine 423 

Side firing 184 

Side-walls of boiler setting •. 215 

Sight-feed lubricators 748 

Silsby rotary engine 500 

Simple and continuous-expansion engines 468 

Single-acting rotative engines 429 

riveted joint 49 

slide-valve, limitations of 653 

stage steam turbine 513 

Siphon condenser 737 

Slide, and sUding valves 630 

Slides or guides 592 

Slip-joint for expansion in steam-pipe 346 

Slipper cross-head 593 



INDEX 821 

PAGE 

Smoke-prevention 25, 208 

Snifting-valves in the cylinder • , 574 

Soil, supporting power of 200, 550 

Solid fly-wheels 623 

Sources of motor energy 2 

Special fuels 234 

Specifications for boiler steels 31 

Specific heat and volumes of gases of combustion 169 

Spherical-unit sectional boiler 138 

Spider piston 577 

Spiral riveted pipe 362 

Spindle-governors 710 

Spray boilers 160 

Spring-governors 707 

Square-piston engine 800 

Staggered riveted joint 55 

Staggered rivets 52 

tubes 91 

Standardization of steam-gauge 274 

Starting an engine 753 

Stationary grates 174 

Stator rings in turbines ' 517 

Staying of domes 77 

tubular and flue boilers 57 

Stays and staying 49-57 

Stead's water-tube boiler ! 129 

Steam-boilers, see Boilers. 

Steam-chimney 77-109 

drums for boilers 73 

engine indicator 442 

gauge for boiler . , , 271 

jacketing 576 

jacket for valve-chest 665 

jet cleaners 282 

making process . 21 

packing 583 

per horse-power , 12, 452 

pipe 335 

pressure-test of boilers 298 

reversing-gecr 682 

riveting-machine 44 

shovel 314 

space in boilers 72 

thrown valves 637 

traps 354 

turbine 505 

Steam-loop for draining steam-pipe 359 

Steam turbine condensers 743 

Steel boilers 30 

crank 608 



822 INDEX 

PAGE 

Steel fly-wheels 626 

specifications for boilers 31 

Steeple compound engine 478 

Steinlen loaded parabolic governor 705 

Step grates 179 

Stephenson link-motion 685 

Stern bearing for marine shaft 613 

Stevens cut-off for river-boat engines 630-672 

Stiffening-rings for flues 96 

Stirling boiler 151 

Stokers, mechanical 181, 309 

Straight-line engine 572 

slipper cross-head 593 

Strains in fly-wheels 622 

Strap of eccentric 614 

Strength of a riveted joint 50 

Stresses in boilers 26, 28, 47 

in steam-pipe 336 

Structure of beam-engines 417 

Stub end 600 

Stuffing box 586 

Subdivided steam-power 764 

Superheating 321 

Supporting power of soils 200, 500 

Surface condenser 724 

Surface blow-off " .' 287 

Sweet pressure-plate 668 

Tandem compound engine 478 

Tangye or Porter bed-plate 562 

Tank bed-plate 560 

Terry steam-turbine 517 

Testing boilers for efficiency 760 

of boilers for strength 298 

boiler-plate 30 

the power-plant for efficiency 760 

Tests of lubricants 745 

rivets 54 

Theory of boiler explosions 301 

Theory of the fly-ball or Watt governor 701 

Thickness of boiler-plate 28 

Thornycroft water-tube boiler 152 

Three- and four- valve gears 657 

Three-way and four-way cock-valves 634 

Throttle valve '. 348 

Throttling engines . : 444 

governors • • • 695 

Through-stays 57 

Throw of slide-valve 637 

Thrust-bearing 611 



INDEX 823 

PAGE 

Thumb swage. , . . o 88 

Tie-rods for boiler-setting „ „ 217 

Time to absorb heat energy , , 304 

Timing of valves , „ 633 

Tit drill for tube-sheets 87 

Torque of the crank , , 398 

Trammel for valve-setting , 645 

Transfer of heat 14, 23 

Transmission of power 765 

Transmitting dynamometer 763 

Trapezoidal ports for cut-off valve. 698 

Traps for drainage of steam-pipe 354 

Travel of a slide-valve 637 

Traveling grates , , 179 

Trip- valve gears , ., 675 

Triple crank 607 

expansion engines 485 

engine diagram 494 

riveted joint 51 

Trunk-engine 380 

Trussed connecting-rod , 400 

Try-cocks for water-level 266 

Tube and fittings boiler 155 

Tube-cleaners 282 

Tube-cutter 90 

Tube-joints for surface condensers 798 

Tubular boiler 84 

Turbine condensers , 743 

Turbines, steam .^. 505 

Turning leverage of crank ' 398 

Twiss engine with loaded governor 797 

Two-flue boiler 94 

valve engines . , 654 

Unequal contraction of boilers 292 

expansion of boilers 292 

Union boiler 132 

joint for pipe 341 

Pacific R. R. boiler 113 

Units of output in a power plant 3 

Upright boiler 120 

Use of Zeuner polar diagram 651 

U. S. cruiser Maine, independent air- and circulating pump. 735 

U. S. formulae for flues and tubes 97 

Vacuum gage 718 

Valve-chest location , 635 

gear for high degrees of expansion , 654 

problems and design 647 

stem 615 



824 INDEX 

PAOB 

Valves and valve-gearing 628 

back pressure 367 

balanced by counter-pressure 669 

for steam pipe. . 34g 

reducing 368 

Valves taking steam internally 669 

Van Stone joint 343 

Variable cam 673 

cut-off engine 695 

valve-gears 695 

Velocity of steam in pipe and ports 338 

Venturi water meter 333 

Vertical engine 406 

frame or bed 568 

tubular sectional boiler 140 

Vibrating piston-engine 789 

Vibration of engine-foundations 552 

Victor reversible filter 291 

V hooks 683 

Volume of steam per horse-power 12 

Wagon-boiler 25 

Wagon-top locomotive boiler Ill 

Wainwright's feed-water heater 324 

Walschaert valve-gear 691 

Ward water-tube boiler 159 

Wasting of boiler-plate 295 

Water column 261 

cooling towers .^. . . . ■ 728 

evaporated per pound of coal ' 216 

gage for boiler 260 

grates 176 

hammer 336 

in engine cyhnder 341-574 

meters ; . 332 

per horsepower per hour 14 

pocket for draining steam-pipe 357 

rate of steam-engine 13 

space in boilers 72 

tube boiler 130 

Waters' spring-governor 707 

Watertown engine bed-plate , 790 

Watt governor 701 

Wear and tear of boilers 292 

Weight of steam per horse-power 12,452 

injection water 719 

Weir's hydrokineter 107 

Welding of boiler-joints 37 

Wells balanced engine 548 

Westinghouse compound single-acting engine 381 



INDEX 825 

PAGE 

Westinghouse compound steam turbine 519 

relief-valve 575 

single-acting engine 434 

Wet and dry air-pump 732 

Wharton-Harrison boiler 138 

Wheel draft 132 

Wheeler's feed-water heater 324 

Wheeler surface condenser . 725 

White steam generator . 162 

Wilkinson mechanical stoker 311 

Willans' single-acting central-valve engine 435 

Winans locomotive cam 673 

Wipers for river-boat engines , 675 

Wire-drawing 629 

Woodbury engine connecting-rod 603 

cross-head 598 

pressure-plate system 794 

Wood's corrugated firebox 118 

flanging machine 36 

Woolf compound engine 475 

Wootton fire-box 112 

Work of cubic foot of steam 452 

Work unit, measurements of 3, 12 

convertible 12 

Worthington boiler 150 

Worthington's ejector condenser 721 

self-cooling condenser tower .' . 729 

Wright spring-governor 707 

Wrist-pin 598 

Wrist-plate of Corliss valve-gear 678 

Wrought-iron boilers 47 

grate bars 176 

Yoke for valve-cam 673 

Yoked piston-rod for crank-motion 245 



Zell sectional boiler, details " 148 

Zeuner polar diagram for slide-valves 647 



'i 



SHORT-TITLE CATALOGUE 

OP THE 

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Freitag's Architectural Engineering 8vo. 

Fireproofing of Steel Buildings 8vo, 

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Non-metallic Minerals : Their Occurrence and Uses. Svo, 

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Worcester and Atkinson's Small Hospitals, Establishment and Maintenance, 

Suggestions for Hospital Architecture, with Plans for a Small Hospital. 

i2mo, 
The World's Columbian Exposition of 1S93 Large 4.to, 



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4 oa 



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I 00 



ARMY AND NAVY. 

Bernadou's Smokeless Powder, Nitrp-cellulose, and the Theory of the Cellulose 

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3 



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(In Press) 

Hopkins's Oil-chemists' Handbook 8vo, 3 00 

Iddings's Rock Minerals 8vo, 5 00 

Jackson's Directions for Laboratory "Work in Physiological Chemistry. .8vo, i 25 
Johannsen's Key for the Determination of Rock-forming Minerals in Thin Sec- 
tions. (In Press) 

Keep's Cast Iroo Svo, 2 50 

Ladd's Manual of Quantitative Chemical Analysis i2mo, i 00 

Landauer's Spectrum Analysis. (Tingle.) Svo, 3 00 

* Langworthy and Austen. The Occurrence of Aluminium in Vegetable 

Products, Animal Products, and Natural Waters Svo, 2 00 

Lassar-Cohn's AppUcation of Some General Reactions to Investigations in 

Organic Chemistry. (Tingle.) ,. . i2mo, i 00 

Leach's The Inspection and Analysis of Food with Special Reference to State 

Control Svo, 

Lob's Electrochemistry of Organic Compounds. (Lorenz.) Svo, 

Lodge's Notes on Assaying and Metallurgical Laboratory Experiments. .. .Svo, 

Low's Technical Method of Ore Analysis Svo, 

Lunge's Techno-chemical Analysis. (Cohn.) i2mo 

* McKay and Larsen's Principles and Practice of Butter-making Svo, 

Maire's Modem Pigments and their vehicles. (In Press.) 

Mandel's Handbook for Bio-chemical Laboratory i2mo, 

* Martin's Laboratory Guide to Qualitative Analysis with the Blowpipe . . i2mo, 
Mason's Water-supply. (Considered Principally from a Sanitary Standpoint.) 

3d Edition, Rewritten Svo, 

Examination of Water. (Chemical and Bacteriological.) i2mo, 

Matthew's The Textile Fibres. 2d Edition, Rewritten Svo, 

Meyer's Determination of Radicles in Carbon Compounds. (Tingle.). .i2mo. 

Miller's Manual of Assaying i2mo. 

Cyanide Process i2mo, 

Minet's Production of Aluminum and its Industrial Use. (Waldo.). . . . i2mo, 

Mixter's Elementary Text-book of Chemistry i2mo, 

Morgan's An Outline of the Theory of Solutions and its Results i2mo, 

Elements of Physical Chemistry i2mo, 

* Physical Chemistry for Electrical Engineers i2mo, 

Morse's Calculations used in Cane-sugar Factories i6mo, morocco, 

* Mu'r's H'story of Chemical Theories and Laws Svo, 

Mulliken's General Method for the Identification of Pure Organic Compounds. 

Vol. I Large Svo, 

O'Driscoll's Notes on the Treatment of Gold Ores 8vo, 

Ostwald's Conversations on Chemistry. Part One. (Ramsey.) i2mo. 

Part Two. (Turnbull.) i2mo, 

* Palmer's Practical Test Book of Chemistry 12mo, 

* Pauli's Physical Chemistry in the Service of Medicine. (Fischer.) . . . . lamo, 

* Penfield's Notes on Determinative Mineralogy and Record of Mineral Tests. 

Svo, paper, 
Pictet's The Alkaloids and their Chemical Constitution. (Biddle.) . . . . .Svo, 

Pinner's Introduction to Organic Chemistry. (Austen.) i2mo, 

Poole's Calorific Power of Fuels Svo, 

Prescott and Winslow's Elements of Water Bacteriology, with Special Refer- 
ence to Sanitary Water Analysis i2mo, 

* Reisig's Guide to Piece-dyeing Svo, ; 

Richards and Woodman's Air, Water, and Food from a Sanitary Standpoint. .Svo, 

Ricketts and Miller's Notes on Assaying Svo, 

Rideal's Sewage and the Bacterial Purification of Sewage Svo, 

Disinfection and the Preservation of Food Svo, 

Riggs's Elementary Mapual for the Chemical Laboratory Svo, 

Robine and Lenglen's Cyanide Industry. (Le Clerc.) Svo, 

5 



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Ruddiman's Incompatibilities in Prescriptions 8vo, 

* Whys in Pharmacy . . . , , . . i2mo, 

Sabin's Industrial and Artistic Technology of Paints and Varnish . .8voj 

Salkowski's Physiological and Pathological Chemistry. (Orndorff.) 8vo, 

Schimpf's Text-book of Volumetric Analysis i2mo. 

Essentials of Volumetric Analysis. , lamo, 

* Qualitative Chemical Analysis Svo, 

Smith's Lecture Notes on Chemistry for Dental Students 8vo, 

Spencer's Handbook for Chemists of Beet-sugar Houses i6mo, morocco 

Handbook for Cane Sugar Manufacturers i6mo. morocco, 

Stockbridge's Rocks and Soils Svo, 

* Tillman's Elementary Lessons in Heat , Svo, 

* Descriptive General Chemistry 8vo» 

Treadwell's Qualitative Analysis. (Hall.), . . .• 8vo^ 

Quantitative Analysis. (HaU.) Svo, 

Turneaure and Russell's Public Water-supplies Svo, 

Van Deventer's Physical Chemistry for Beginners. (Boltwood.) i2mo, 

* Walke's Lectures on Explosives . . .Svo, 

Ware's Beet-sugar Manufacture and Refining. Vol. I Small Svo, 

Vol.11 SmallSvo, 

Washington's Manual of the Chemical Analysis of Rocks Svo, 

Weaver's Military Explosives Svo, 

Wehrenfennig's Analysis and Softening of Boiler Feed-Water Svo, 

Wells's Laboratory Guide in«Qualitative Chemical Analysis Svo, 

Short Course in Inorganic Qualitative Chemical Analysis for Engineering 

Students i2mo, 

Text-book of Chemical Arithmetic i2mo, 

Whipple's Microscopy of Drinking-water Svo, 

Wilson's Cyanide Processes i2mo, 

Chlorination Process i2mo, 

Winton's Microscopy of Vegetable Foods Svo, 

Wulling's Elementary Course in Inorganic, Pharmaceutical, and Medical , 
Chemistry - i2mo, 



CIVIL ENGINEERING. 

BRIDGES AND ROOFS. HYDRAULICS. MATERIALS OF ENGINEERING 
RAILWAY ENGINEERING. 

Baker's Engineers* Surveying Instruments i2mo, 

Bixby's Graphical Computing Table Paper 19^X24^ inches. 

Breed and Hosmer's Principles and Practice of Surveying . .Svo, 

* Biirr's Ancient and Modem Engineering and the Isthmian Canal Svo, 

Comstock's Field Astronomy for Engineers Svo, 

* Corthell's Allowable Pressures on Deep Foundations i2mo, 

CrandaU's Text-book on Geodesy and Least Squares Svo, 

Davis's Elevation and Stadia Tables. Svo, 

Elliott's Engineering for Land Drainage i2mo. 

Practical Farm Drainage i2mo, 

*Fiebeger's Treatise on Civil Engineering Svo, 

Flemer's Phototopographic Methods and Instruments Svo, 

Folwell's Sewerage. (Designing and Maintenance.) Svo, 

Freitag's Architectural Engineering. 2d Edition, Rewritten Svo, 

French and Ives's Stereotomy Svo, 

Goodhue's Municipal Improvements i2mo. 

Gore's Elements of Geodesy 8vo, 

* Hauch and Rice's Tables of Quantities for Preliminary Estimates l2mo, 

Hayford's Text-book of Geodetic Astronomy Svo, 

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Bering's Ready Reference Tables (Conversion Factors) i6mo, morocco. 

Bowe's Retaining Walls for Earth i2mo, 

Hoyt and Grover's River Discharge 8vo, 

* Ives's Adjustments of the Engineer's Transit and Level i6mo, Bds. 

Ives and Hilts's Problems in Surveying i6mo, morocco, 

Johnson's (J. B.) Theory and Practice of Surveying Small 8vo, 

Johnson's (L. J.) Statics by Algebraic and Graphic Methods 8vo, 

Laplace's Philosophical Essay on Probabilities. (Truscott and Emory.) . i2mo, 
Mahan's Treatise on Civil Engineering. (1873.) (Wood.) 8vo, 

* Descriptive Geometry. 8vo, 

Merriman's Elements of Precise Surveying and Geodesy 8vo, 

Merriman and Brooks's Handbook for Surveyors i6mo, morocco, 

Nugent's Plane Surveying 8vo, 

Ogden's Sewer Design i2mo, 

Parsons's Disposal of Municipal Refuse. 8vo, 

Patton's Treatise on Civil Engineering . .8vo half leather, 

Reed's Topographical Drawing and Sketching 4to, 

Rideal's Sewage and the Bacterial Purification of Sewage 8vo, 

Jliemer's Shaft-sinking under Difficult Conditions. (Coming and Peele) . .8vo, 

•Siebert and Biggin's Modern Stone-cutting and Masonry 8vo, 

-Smith's Manual of Topographical Drawing. (McMillan.) 8vc, 

^ondericker's Graphic Statics, with Applications to Trusses, Beams, and Arches. 

8vo, 

Taylor and Thompson's Treatise on Concrete, Plain and Reinforced 8vo, 

Tracy's Plane surveying i6mo, morocco, 

* Trautwine's Civil Engineer's Pocket-book i6mo, morocco, 

Tenable's Garbage Crematories in America , .8vo, 

Wait's Engineering and Architectural Jurisprudence. 8vo, 

Sheep, 
Law of Operations Preliminary to Construction in Engineering and Archi- 
tecture 8vo, 

Sheep, 

Law of Contracts 8vo, 

"Warren's Stereotomy — Problems in Stone-cutting 8vo, 

Webb's Problems in the Use and Adjustment of Engineering Instruments. 

i6mo, morocco, 
Wilson's Topographic Surveying 8vo, 

BRIDGES AND ROOFS. 

Boiler's Practical Treatise on the Construction of Iron Highway Bridges. .8vo, 

JBurr and Falk's Influence Lines for Bridge and Roof Computations 8vo, 

Design and Construction of Metallic Bridges 8vo, 

JDu Bois's Mechanics of Engineering. Vol. II Small 4to, 

Foster's Treatise on Wooden Trestle Bridges 4to, 

Fowler's Ordinary Foundations 8vo, 

Greene's Roof Trusses 8vo, 

Bridge Trusses 8vo, 

Arches in Wood, Iron, and Stone 8vo, 

Grimm's Secondary Stresses in Bridge Trusses. (In Press, ) 

Howe's Treatise on Arches 8vo, 

Design of Simple Roof- trusses in Wood and Steel 8vo, 

Symmetrical Masonry Arches 8vo, 

Johnson, Bryan, and Turneaure's Theory and Practice in the Designing of 

Modern Framed Structures Small 4to, 10 00 

Merriman and Jacoby's Text- book on Roofs and Bridges; 

Part I. Stresses in Simple Trusses 8vo, 2 50 

Part II. Graphic Statics 8vo, 2 50 

Part III. Bridge Design _. 8vo, 2 50 

Part IV. Higher Structures ; 8vo, 2 50 

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Morison's Memphis Bridge. 4to, lo oo 

Waddell's De Pontibus, a Pocket-book for Bridge Engineers . . i6mo, morocco, 2 00 

* Specifications for Steel Bridges i2mo, 50 

Wright's Designing of Draw-spans. Two parts in one volume 8vo, 3 sa 

HYDRAULICS. 

Barnes's Ice Formation 8vo, 3 00 

Bazin's Experiments upon the Contraction of the Liquid Vein Issuing from 

an Orifice, (Trautwine.). , 8vo, 2 00 

Bovey's Treatise on Hydraulics 8vo, 5 00 

Church's Mechanics of Engineering 8vo, 6 oo- 

Diagrams of Mean Velocity of Water in Open Channels paper, 1 50 

Hydrauhc Motors. . , 8vo, 2 00 

Coffin's Graphical Solution of Hydraulic Problems i6mo, morocco, 2 50 

Flather's Dynamometers, and the Measurement of Power i2mo, 3 00 

Folwell's Water-supply Engineering 8vo, 4 00 

Frizell's Water-power , 8vo, 5 oo- 

Fuertes's Water and Public Health i2mo, i 50 

Water-filtration Works i2mo. 2 50 

Ganguillet and Kutter's General Formula for the Uniform Flow of Water in 

Rivers and Other Channels. (Hering and Trautwine.) 8vo, 4 oa 

Hazen's Clean Water and How to Get It Large i2mo, l 5o 

Filtration of Public Water-supply 8vo, 3 00 

Hazlehurst's Towers and Tanks for Water- works 8vo, 2 50 

Herschel's 115 Experiments on the Carrying Capacity of Large, Riveted, Metal 

Conduits 8vo, 2 oo 

* Hubbard and Kiersted's Water- works Management and Maintenance.. Svo, 4 vo 
Mason's Water-supply. (Considered Principally from a Sanitary Standpoint.) 

8vo,^ 4 oO" 

Merriman's Treatise on Hydraulics 8vo, 5 oa 

* Michie's Elements of Analytical Mechanics 8vo, 4 oo 

Schuyler's Reservoirs for Irrigation, Water-power, and Domestic Water- 
supply Large 8vo, 5 oa 

* Thomas and Watt's Improvement of Rivers 4to, 6 00 

Turneaure and Russell's Public Water-supplies Svo, 5 oa 

Wegmann's Design and Construction of Dams. 5th Edition, enlarged. . .4to, 6 oa 

Water-supply of the City of New York from 1658 to 1895 4to, 10 oa 

Whipple's Value of Pure Water. . Large i2mo, i oa 

Williams and Hazen's Hydrauhc Tables , 8vo, i 5a 

Wilson's Irrigation Engineering , Small 8vo, 4 oa 

Wolff's Windmill as a Prime Mover 8vo, 3 oa 

Wood's Turbines 8vo, 2 5a 

Elements of Analytical Mechanics Svo, 3 oa 

MATERIALS OF ENGINEERING. 

Baker's Treatise on Masonry Construction Svo, 5 oa 

Roads and Pavements Svo, 5 oa 

Black's United States Public Works Oblong 4to, 5 oa 

* Bovey's Strength of Materials and Theory of Structures Svo, 7 5a 

Burr's Elasticity and Resistance of the Materials of Engineering Svo, 7 5a 

Byrne's Highway Construction Svo, 5 oa 

Inspection of the Materials and Workmanship Employed in Construction. 

i6mo, 3 oa 

Church's Mechanics of Engineering Svo, 6 oa 

Du Bois's Mechanics of Engineering. Vol. I Small 4to. 7 50 

♦Eckel's Cements, Limes, and Plasters Svo, 6 oc 

8 



Jolmson's Materials of Construction Large 8vo, 

Fowler's Ordinary Foundations 8vo, 

Graves's Forest Mensuration 8vo, 

* Greene's Structural Mechanics 8vo, 

Keep's Cast Iron 8vo, 

Lanza's Applied Mechanics Svo, 

Martens's Handbook on Testing Materials. (Henning.) 2 vols . .8vo, 

Maurer's Technical Mechanics 8vo, 

Merrill's Stones for Building and Decoration 8vo, 

Merriman's Mechanics of Materials 8vo, 

* Strength of Materials .^ i2mo, 

Metcalf's Steel. A Manual for Steel-users i2mo, 

Patton's Practical Treatise on Foundations Svo, 

Richardson's Modern Asphalt Pavements Svo, 

Richey's Handbook for Superintendents of Construction i6mo, mor., 

* Ries's Clays: Their Occurrence, Properties, and Uses Svo, 

Rockwell's Roads and Pavements in France i2mo, 

Sabin's Industrial and Artistic Technology of Paints and Varnish 8vc, 

*Schwarz's Longleaf Pine in Virgin Forest ., i2mo, 

Smith's Materials of Machines i2mo. 

Snow's Principal Species of Wood . Svo, 

Spalding's Hydraulic Cement i2mo. 

Text-book on Roads and Pavements i2mo, 

Taylor and Thompson's Treatise on Concrete, Plain and Reinforced Svo, 

Thurston's Materials of Engineering. 3 Parts Svo, 

Part I. Non-metallic Materials of Engineering and Metallurgy Svo, 

Part li. Iron and Steel Svo, 

Part III. A Treatise on Brasses, Bronzes, and Other Alloys and their 

Constituents Svo, 

Tillson's Street Pavements and Paving Materials Svo, 

Tumeaure and Maurer's Principles of Reinforced Concrete Construction. Svo, 
Waddell's De Pontibus. (A Pocket-book for Bridge Engineers.). . i6mo, mor., 

* Specifications for Steel Bridges i2mo. 

Wood's (De V.) Treatise on the Resistance of Materials, and an Appendix on 

•the Preservation of Timber Svo, 

Wood's (De V.) Elements of Analytical Mechanics Svo, 

Wood's (M. P.) Rustless Coatings: Corrosion and Electrolysis of Iron and 

Steel Svo, 4 00 



RAILWAY ENGINEERING. 

Andrew's Handbook for Street Railway Engineers 3x5 inches, morocco, 

Berg's Buildings and Structures of American Railroads 4to, 

Brook's Handbook of Street Railroad Location i6mo, morocco. 

Butt's Civil Engineer's Field-book i6mo, morocco, 

Crandall's Transition Curve i6mo, morocco. 

Railway and Other Earthwork Tables Svo, 

Crookett's Methods for Earthwork Computations. (In Press) 

Dawson's "Engineering" and Electric Traction Pocket-book. . i6mo, morocco 

Dredge's History of the Pennsylvania Railroad: (1879) Paper, 

Fisher's Table of Cubic Yards Cardboard, 

Godwin's Railroad Engineers' Field-book and Explorers' Guide. . . i6mo, mor., 
Hudson's Tables for Calculating the Cubic Contents of Excavations and Em- 
bankments Svo, 

Molitor and Beard's Manual for Resident Engineers i6mo, 

Nagle's Field Manual for Raibroad Engineers i6mo, morocco, 

Philbrick's Field Manual for Engineers i6mo, morocco, 

Raymond's Elements of Railroad Engineering. (In Press.) 

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Searles's Field Engineering i6mo, morocco, 3 00 

Railroad Spiral i6mo, morocco, i 50 

Taylor's Prismoidal Formulae and Earthwork 8vo, i 50 

* Trautwine's Method of Calculating the Cube Contents of Excavations and 

Embankments by the Aid of Diagrams 8vo, 2 00 

The Field Practice of Laying Out Circular Curves for Railroads. 

i2mo, morocco, 2 50 

Cross-section Sheet Paper, 25 

Webb's Railroad Construction i6mo, morocco, 5 00 

Economics of Railroad Construction .Large i2mo, 2 50 

Wellington's Economic Theory of the Location of Railways Small 8vo^ s 00 



DRAWING. 

Barr's Kinematics of Machinery Svo, 2 50 

* Bartlett's Mechanical Drawing 8vo, 3 00 

* " " " Abridged Ed Svo, 1 50 

Coolidge's Manual of Drawing 8vo, paper, i 00 

Coolidge and Freeman's Elements of General Drafting for Mechanical Engi- 
neers Oblong 4to, 2 50 

Durley's Kinematics of Machines Svo, 4 00 

Emch's Introduction to Projective Geometry and its Applications Svo, 2 50 

Hill's Text-book on Shades and Shadows, and Perspective Svo, 2 00 

Jamison's Elements of Mechanical Drawing Svo, 2 50 

Advanced Mechanical Drawing Svo, 2 00 

Jones's Machine Design: 

Part I. Kinematics of Machinery Svo, i 50 

Part II. Form, Strength, and Proportions of Parts Svo, 3 00 

MacCord's Elements of Descriptive Geometry Svo, 3 00 

Kinematics; or. Practical Mechanism Svo, 5 00 

Mechanical Drawing 4to, 4 00 

Velocity Diagrams Svo, i 50 

MacLeod's Descriptive Geometry Small Svo, i 50 

* Mahan's Descriptive Geometry and Stone-cutting Svo, i 50 

Industrial Drawing. (Thompson.) !8vo, 3 50 

Moyer's Descriptive Geometry Svo, 2 00 

Reed's Topographical Drawing and Sketching 4to, 5 00 

Reid's Course in Mechanical Drawing Svo, 2 00 

Text-book of Mechanical Drawing and Elementary Machine Design. Svo, 3 00 

Robinson's Principles of Mechanism Svo, 3 00 

Schwamb and Merrill's Elements of Mechanism Svo, 3 00 

Smith's (R. S.) Manual of Topographical Drawing. (McMillan.) Svo, 2 50 

Smith (A. W.) and Marx's Machine Design Svo, 3 00 

* Titsworth's Elements of Mechanical Drawing Oblong Svo, i 25 

Warren's Elements of Plane and Solid Free-hand Geometrical Drawing. i2mo, i 00 

Drafting Instruments and Operations i2mo, i 25 

Manual of Elementary Projection Drawing i2mo, i 50 

Manual of Elementary Problems in the Linear Perspective of Form and 

Shadow i2mo, 1 00 

Plane Problems in Elementary Geometry i2mo, i 25 

Elements of Descriptive Geometry, Shadows, and Perspective Svo, 3 50 

General Problems of Shades and Shadows ; Svo, 3 00 

Elements of Machine Construction and Drawing Svo, 7 50 

Problems, Theorems, and Examples in Descriptive Geometry Svo, 2 50 

Weisbach's Kinematics and Power of Transmission. (Hermann and 

Klein.) Svo, 5 Oq 

Whelpley's Practical Instruction in the Art of Letter Engraving i2mo, 2 00 

Wilson's (H. M.) Topographic Surveying Svo, 3 50 

10 



Wilson's (V. T.) Free-hand Perspective 8vo, 2 so 

Wilson's (V. T.) Free-hand Lettering 8vo, 1 00 

Woolf's Elementary Course in Descriptive Geometry Large 8vo, 3 00 

ELECTRICITY AND PHYSICS. 

* Abegg's Theory of Electrolytic Dissociation. (Von Ende.) i2mo, 

Anthony and Brackett's Text-book of Physics. (Magie.) Small Svo, 

Anthony's Lecture-notes on the Theory of Electrical Measurements. . . . i2mo, 
Benjamin's History of Electricity Svo, 

Voltaic Cell Svo, 

Betts's Lead Refining and Electrolysis. (In Press.) 

Classen's Quantitative Chemical Analysis by Electrolysis. (Boltwood.).8vo, 

* Collins's Manual of Wireless Telegraphy i2mo, 

Morocco, 
Crehore and Squier's Polarizing Photo-chronograph Svo, 

* Danneel's Electrochemistry. (Merriam.) i2mo, 

Dawson's "Engineering" and Electric Traction Pocket-book. i6mo, morocco, 
Dolezalek's Theory of the Lead Accumulator (Storage Battery). (Von Ende.) 

i2mo, 

Duhem's Thermodynamics and Chemistry. (Burgess.). Svo, 

Flather's Dynamometers, and the Measurement of Power i2mo, 

Gilbert's De Magnete. (Mottelay.) Svo, 

Hanchett's Alternating Currents Explained i2mo, 

Bering's Ready Reference Tables (Conversion Factors) lomo, morocco, 

Hobart and Ellis's High-speed Dynamo Electric Machinery. (In Press.) 

Holman's Precision of Measurements Svo, 

Telescopic Mirror-scale Method, Adjustments, and Tests. . . .Large Svo, 
Karapetoff's Experimental Electrical Engineering. (In Press.) 

Kinzbrunner's Testing of Continuous-current Machines Svo, 

Landauer's Spectrum Analysis. (Tingle.) Svo, 

Le Chatelier's High-temperature Measurements. (Boudouard — Burgess.) i2mo. 
Lob's Electrochemistry of Organic Compounds. (Lorenz. ) Svo, 

* Lyons's Treatise on Electromagnetic Phenomena. Vols. I. and II. Svo, each, 

* Michie's Elements of Wave Motion Relating to Sound and Light Svo, 

Niaudet's Elementary Treatise on Electric Batteries. (Fishback.) i2mo, 

Norris's Introduction to the Study of Electrical Engineering. (In Press.) 

* Parshall and Hobart's Electric Machine Design 4to, half morocco, 12 50 

Reagan's Locomotives: Simple, Compound, and Electric. New Edition. 

Large 12 mo, 

* Rosenberg's Electrical Engineering. (Haldane Gee — Kinzbrunner.). . .Svo, 

Ryan, Norris, and Hoxie's Electrical Machinery. Vol. I. . . ." Svo, 

Thurston's Stationary Steam-engines. Svo, 

* Tillman's Elementary Lessons in Heat Svo, 

Tory and Pitcher's Manual of Laboratory Physics Small Svo, 

Ulke's Modern Electrolytic Copper Refining Svo, 

LAW. 

* Davis's Elements of Law Svo, 

* Treatise on the Military Law of United States Svo, 

* Sheep, 

* Dudley's Military Law and the Procedure ol Courts-martial . . . Larg-e i2mo. 

Manual for Courts-martial i6mo, morocco. 

Wait's Engineering and Architectural Jurisprudence Svo, 

Sheep, 
Law of Operations Preliminary to Construction in Engineering and Archi- 
tecture Svo 

Sheep, 

Law of Contracts. . Svo, 

Winthrop's Abridgment of Military Law i2mo, 

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MANUFACTURES. 

Bemadou's Smokeless Powder — Nitro-cellulose and Theory of the Cellulose 

Molecule i2mo, 

Bolland's Iron Founder 1 2mo, 

The Iron Founder," Supplement 1 2mo, 

Encyclopedia of Founding and Dictionary of Foundry Terms Used in the 
Practice of Moulding i2mo, 

* Claassen's Beet-sugar Manufacture. (Hall and RoLfe.) 8vo, 

* Eckel's Cements, Limes, and Plasters 8vo, 

Eissler's Modern High Explosives 8vo, 

Effront's Enzymes and their Applications. (Prescott.) Svo, 

Fitzgerald's Boston Machinist i2mo, 

Ford's Boiler Making for Boiler Makers i8mo. 

Herrick's Denatured or Industrial Alcohol ..8vo, 4 00 

Honey and Ladd's Analysis of Mixed Paints, Color Pigments, and Varnishes. 

(In Press.) 

Hopkins's Oil-chemists' Handbook. . . . ; .8vo, 

Keep's Cast Iron 8vOi, 

Leach's The Inspection and Analysis of Food with Special Reference to State 
Control Large 8vo, 

* McKay and Larsen's Principles and Practice of Butter-making 8vo, 

Maire's Modern Pigments and their Vehicles. (In Press.) 

Matthews's The Textile Fibres. 2d Edition, Rewritten 8vo, 

Metcalf's Steel. A Maunal for Steel-users i2mo, 

Metcalfe's Cost of Manufactures — And the Administration of Workshops 8vo, 

Meyer's Modern Locomotive Construction 4to, 

Morse's Calculations used in Cane-sugar Factories i6mo, morocco, 

* Reisig's Guide to Piece-dyeing 8vo, 

Rice's Concrete-block Manufacture 8vo, 

Sabin's Industrial and Artistic Technology of Paints and Varnish 8vo, 

Smith's Press-working of Metals 8vo, • 

Spalding's Hydraulic Cement i2mo, 

Spencer's Handbook for Chemists of Beet-sugar Houses i6mo, morocco, 

Handbook for Cane Sugar Manufacturers i6mo, morocco, 

Taylor and Thompson's Treatise on Concrete, Plain and Reinforced 8vo, 

Thurston's Manual of Steam-boilers, their Designs, Construction and Opera- 
tion 8vo, 

Ware's Beet-sugar Manufacture and Refining. Vol. I Small 8vo, 

Vol.11 8vo, 

Weaver's Military Explosives 8vo, 

West's American Foundry Practice i2mo, 

Moulder's Text-book i2mo, 

Wolff's Windmill as a Prime Mover 8vo, 

Wood's Rustless Coatings: Corrosion and Electrolysis of Iron and Steel .8vo, 

MATHEMATICS. 

Baker's Eniptic Functions Svo, i 50 

Briggs's Elements of Plane Analytic Geometry i2mo, i 00 

Buchanan's Plane and Spherical Trigonometry, (In Press.) 

Compton's Manual of Logarithmic Computations i2mo,. i 50 

Davis's Introduction to the Logic of Algebra Svo, i so 

* Dickson's College Algebra Large L2mo, i 50 

* Introduction to the Theory of Algebraic Equations' Large i2mo, 1 25 

Emch's Introduction to Projective Geometry and its Applications Svo, 2 50 

Halsted's Elements of Geometry Svo, 1 75 

Elementary Synthetic Geometry Svo, 1 50 

* Rational Geometry i2mo, i SO 

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♦Johnson's (J. B.) Three-place Logarithmic Tables: Vest-pocket size, paper, 

loo copies for 

* Mounted on heavy cardboard, 8 X lo inches, 

lo copies for 
Johnson's (W. W.) Elementary Treatise on Differential Calculus. .Small 8vo, 

Elementary Treatise on the Integral Calculus Small Svo, 

Johnson's (W. W.) Curve Tracing in Cartesian Co-ordinates i2mo, 

Johnson's (W. W.) Treatise on Ordinary and Partial Differential Equations. 

Small Svo, 

Johnson's Treatise on the Integral Calculus Small Svo, 

Johnson's (W. W.) Theory of Errors and the Method of Least Squares. i2mo, 

* Johnson's (W. W.) Theoretical Mechanics i2mo, 

Laplace's Philosophical Essay on Probabilities. (Truscott and Emory. ).i2mo, 

* Ludlow and Bass. Elements of Trigonometry and Logarithmic and Other 

Tables Svo, 

Trigonometry and Tables published separately Each, 

* Ludlow's Logarithmic and Trigonometric Tables Svo, 

Manning's IrrationalNumbers and their Representation bySequences and Series 

i2mo, I 25 
Mathematical Monographs. Edited by Mansfield Merriman and Robert 

S. Woodward Octavo, each i 00 

No. I. History of Modern Mathematics, by David Eugene Smith. 
No. 2. Synthetic Projective Geometry, by George Bruce Halsted. 
Ko. 3. Determinants, by Laenas Gifford Weld. No. 4. Hyper- 
bolic Functions, by James McMahon. No, So Harmonic Func- 
tions, by William E. Byerly. No. 6. Grassmann's Space Analysis, 
by Edward W. Hyde. No. 7. Probability and Theory of Errors, 
by Robert S. Woodward. No. 8. Vector Analysis and Quaternions, 
by Alexander Macfarlane. No. 9. Differential Equations, by- 
William Woolsey Johnson. No. 10. The Solution of Equations, 
by Mansfield Merriman. No. 11. Functions of a Complex Variable, 
by Thomas S. Fiske. 

Maurer's Technical Mechanics Svo, 4 00 

Merriman's Method of Least Squares Svo, 2 00 

Rice and Johnson's Elementary Treatise on the Differential Calculus. . Sm. Svo, 3 00 
Differential and Integral Calculus. 2 vols, in one Small Svo, 2 50 

* Veblen and Lennes's Introduction to the Real Infinitesimal Analysis of One 

Variable Svo, 2 00 

Wood's Elements of Co-ordinate Geometry Svo, 2 00 

Trigonometry: Analytical, Plane, and Spherical i2mo, i 00 



MECHANICAL ENGINEERING. 

MATERIALS OF ENGINEERING, STEAM-ENGINES AND BOILERS. 

Bacon's Forge Practice i2mo, 

Baldwin's Steam Heating for Buildings i2mo, 

Barr's Kinematics of Machinery Svo, 

* Bartlett's Mechanical Drawing Svo, 

* " " " Abridged Ed Svo, 

Benjamin's Wrinkles and Recipes i2mo. 

Carpenter's Experimental Engineering Svo, 

Heating and Ventilating Buildings Svo, 

Clerk's Gas and Oil Engine Small Svo, 

CooUdge's Manual of Drawing Svo, paper, 

Coohdge and Freeman's Elements of General Drafting for Mechanical En- 
gineers Oblong 4to, 

Cromwell's Treatise on Toothed Gearing i2mo. 

Treatise on Belts and Pulleys i2mo, 

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Durley's Kinematics of Machines 8vo, 

Flather's Dynamometers and the Measurement of Power. i2mo. 

Rope Driving i2mo. 

Gill's Gas and Fuel Analysis for Engineers i2mo, 

Hall's Car Lubrication i2mo, 

Hering's Ready Reference Tables (Conversion Factors) i6mo, morocco, 

Button's The Gas Engine. . 8vo, 

Jamison's Mechanical Drawing 8vo, 

Jones's Machine Design: 

Part I. Kinematics of Machinery 8vo, 

Part II. Form, Strength, and Proportions of Parts 8vo, 

Kent's Mechanical Engineers' Pocket-book i6mo, morocco, 

Kerr's Power and Power Transmission 8vo, 

Leonard's Machine Shop, Tools, and Methods 8vo, 

* Lorenz's Modern Refrigerating Machinery. (Pope, Haven, and Dean.) . . 8vo, 
MacCord's Kinematics; or, Practical Mechanism 8vo, 

Mechanical Drawing 4to, 

Velocity Diagrams , 8vo, 

MacFar land's Standard Reduction Factors for Gases 8vo, 

Mahan's Industrial Drawing. (Thompson.) 8vo, 

Poole's Calorific Power of Fuels .8vo, 

Reid's Course in Mechanical Drawing 8vo, 

Text-book of Mechanical Drawing and Elementary Machine Design. 8vo, 

Richard's Compressed Air i2mo, 

Robinson's Principles of Mechanism 8vo, 

Schwamb and Merrill's Elements of Mechanism 8vo, 

Smith's (O.) Press-working of Metals 8vo, 

Smith (A. W.) and Marx's Machine Design 8vo, 

Thurston's Treatise on Friction and Lost Work in Machinery and Mill 
Work 8vo, 

Animal as a Machine and Prime Motor, and the Laws of Energetics . i2mo, 

Tillson's Complete Automobile Instructor i6mo, 

Morocco, 

Warren's Elements of Machine Construction and Drawing 8vo, 

Weisbach's Kinematics and the Power of Transmission. (Herrmann — 
Klein.) 8vo, 

Machinery of Transmission and Governors. (Herrmann — Klein.). .8vo, 

Wolff's Windmill as a Prime Mover 8vo, 

Wood's Turbines 8vo, 

MATERIALS OF ENGINEERING. 

* Bovey's Strength of Materials and Theory of Structures 8vo, 7 50 

Burr's Elasticity and Resistance of the Materials of Engineering. 6th Edition. 

Reset 8vo, 

Church's Mechanics of Engineering 8vo, 

* Greene's Structural Mechanics 8vo, 

Johnson's Materials of Construction 8vo, 

Keep's Cast Iron • 8vo, 

Lanza's AppUed Mechanics 8vo, 

Martens's Handbook on Testing Materials. (Henning.) 8vo, 

Maurer's Technical Mechanics 8vo, 

Merriman's Mechanics of Materials 8vo, 

* Strength of Materials i2mo, 

Metcalf's Steel. A Manual for Steel-users i2mo, 

Sabin's Industrial and Artistic Technology of Paints and Varnish Svo, 

Smith's Materials of Machines i2mo, 

Thurston's Materials of Engineering 3 vols., 8vo, 

Part II. Iron and Steel 8vo, 

Part III. A Treatise on Brasses, Bronzes, and Other Alloys and their 
Constituents 8vo, 

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Wood's (De V.) Treatise on the Resistance of Materials and an Appendix on 

the Preservation of Timber 8vo, 2 00 

Elements of Analytical Mechanics 8vo, 3 00 

Wood's (M. P.) Rustless Coatings: Corrosion and Electrolysis of Iron and 

Steel 8vo, 4 00 

STEAM-ENGINES AND BOILERS. 

Berry's Temperature-entropy Diagram i2mo, i 25 

Carnot's Reflections on the Motive Power of Heat. (Thurston.) i2mo, i 50 

Creighton's Steam-engine and other Heat-motors 8vo, 500 

Dawson's "Engineering" and Electric Traction Pocket-book. . . .i6mo, mor., 5 00 

Ford's Boiler Making for Boiler Makers i8mo, i 00 

Goss's Locomotive Sparks 8vo, 2 00 

Locomotive Performance 8vo, 5 00 

Hemenway's Indicator Practice and Steam-engine Economy .i2mo, 2 00 

Button's Mechanical Engineering of Power Plants 8vo, 5 00 

Heat and Heat-engines 8vo, 5 00 

Kent's Steam boiler Economy 8vo, 4 00 

Kneass's Practice and Theory of the Injector 8vo, i 50 

MacCord's Slide-valves 8vo, 2 00 

Meyer's Modern Locomotive Construction 4to, 10 00 

Peabody's Manual of the Steam-engine Indicator 12 mo. i 50 

Tables of the Properties of Saturated Steam and Other Vapors 8vo, i 00 

Thermodynamics of the Steam-engine and Other Heat-engines 8vo, 5 00 

Valve-gears for Steam-engines 8vo, 2 50 

Peabody and Miller's Steam-boilers 8vo, 4 00 

Pray's Twenty Years with the Indicator Large 8vo, 2 50 

Pupin's Thermodynamics of Reversible Cycles in Gases and Saturated Vapors. 

(Osterberg.) i2mo, i 25 

Reagan's Locomotives: Simple, Compound, and Electric. New Edition. 

Large i2mo, 3 50 

Sinclair's Locomotive Engine Running and Management i2mo, 2 00 

Smart's Handbook of Engineering Laboratory Practice i2mo, 2 50 

Snow's Steam-boiler Practice 8vo, 3 00 

Spangler's Valve-gears 8vo, 2 50 

Notes on Thermodynamics i2mo, i 00 

Spangler, Greene, and Marshall's Elements of Steam-engineering 8vo, 3 00 

Thomas's Steam-turbines 8vo, 3 50 

Thurston's Handy Tables 8vo, i 50 

Manual of the Steam-engine 2 vols., 8vo, 10 00 

Part I. History, Structure, and Theoiy. 8vo, 6 00 

Part 11. Design, Construction, and Operation 8vo, 6 00 

Handbook of Engine and Boiler Trials, and the Use of the Indicator and 

the Prony Brake 8vo, 5 00 

Stationary Steam-engines 8vo, 2 50 

Steam-boiler Explosions in Theory and in Practice i2mo, i 50 

Manual of Steam-boilers, their Designs, Construction, and Operation . 8vo, 5 00 

Wehrenfenning'sAnalysisandSofteningof Boiler Feed-water (Patterson) 8vo, 4 00 

Weisbach's Heat, Steam, and Steam-engines. (Du Bois.) 8vo, 5 00 

Whitham's Steam-engine Design 8vo, 5 00 

Wood's Thermodynamics, Heat Motors, and Refrigerating Machines. . .8vo, 4 00 



MECHANICS AND MACHINERY. 

Barr's Kinematics of Machinery 8vo, 2 50 

* Bovey's Strength of Materials and Theory of Structures 8vo, 7 50 

Chase's The Art of Pattern-making i2nio, 2 50 

15 



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Church's Mechanics of Engineering 8vo , 

Notes and Examples in Mechanics 8vo, 

Compton's First Lessons in Metal-working i2mo, 

Compton and De Groodt's The Speed Lathe i2mo, 

Cromwell's Treatise on Toothed Gearing i2mo, 

Treatise on Belts and Pulleys i2mo, 

Dana's Text-book of Elementary Mechanics for Colleges and Schools. .i2mo. 

Dingey's Machinery Pattern Making i2mo, 

Dredgers Record of the Transportation Exhibits Building of the World's 

Columbian Exposition of 1893 4to half morocco, 5 00 

Du Bois's Elementary Principles of Mechanics : 

Vol. I. Kinematics 8vo, 

Vol. II. Statics. . 8vo, 

Mechanics of Engineering. Vol. I Small 4to, 

Vol. II Small 4to, 

Durley's Kinematics of Machines 8vo, 

Fitzgerald's Boston Machinist i6mo, 

Flather's Dynamometers, and the Measurement of Power i2mo. 

Rope Driving i2mo, 

Goss's Locomotive Sparks 8vo, 

Locomotive Performance 8vo, 

* Greene's Structural Mechanics Svo, 

Hall's Car Lubrication i2mo, 

Hobart and Ellis's High-speed Dynamo Electric Machinery. (In Press.) 

Holly's Art of Saw Filing i8mo, 7S 

James's Kinematics of a Point and the Rational Mechanics of a Particle. 

Small Svo, 2 00 

* Johnson's (W. W.) Theoretical Mechanics i2mo, 3 00 

Johnson's (L. J.) Statics by Graphic and Algebraic Methods Svo, 2 00 

Jones's Machine Design: 

Part I. Kinematics of. Machinery .8vo, i 50 

Part II. Form, Strength, and Proportions of Parts 8vo, . 3 00 

Kerr's Power and Power Transmission 8vo, 2 00 

Lanza's Applied Mechanics 8vo, 7 50 

Leonard's Machine Shop, Tools, and Methods Svo, 4 00 

* Lorenz's Modern Refrigerating Machinery. (Pope, Haven, iand Dean.). Svo, 4 00 
MacCord's Kinematics; or, Practical Mechanism Svo, 5 00 

Velocity Diagrams Svo, i so 

* Martin's Text Book on Mechanics, Vol. I, Statics i2mo, i 25 

* Vol. 2, Kinematics and Kinetics . .i2mo, 1 so 

Maurer's Technical Mechanics Svo, 4 00 

Merriman's Mechanics of Materials Svo, s 00 

* Elements of Mechanics i2mo, i 00 

* Michie's Elements of Analytical Mechanics • Svo, 4 00 

* Parshall and Hobart's Electric Machine Design 4to, half morocco, 12 50 

Reagan's Locomotives : Simple, Compound, and Electric. New Edition. 

Large i2mo, 3 5o 
Reid's Course in Mechanical Drawing Svo, 2 00 

Text-book of Mechanical Drawing and Elemeiitary Machine Design. Svo, 3 00 

Richards's Compressed Air. i2mo, i 50 

Robinson's Principles of Mechanism Svo, 3 00 

Ryan, Norris, and Hoxie's Electrical Machinery. Vol. I .Svo, 2 50 

Sanborn's Mechanics: Problems Large i2mo, i 50 

Schwamb and Merrill's Elements of Mechanism Svo, 3 00 

Sinclair's Locomotive-engine Running and Management i2mo, 2 00 

Smith's (O.) Press-working of Metals Svo, 3 00 

Smith's (A. W.) Materials of Machines i2mo, i 00 

Smith (A. W.) and Marx's Machine Design Svo, 3 00 

Sorer s Carbureting and Combustion of Alcohol Engines. (Woodward and 

Preston.) Large Svo, 3 00 

16 



Spangler, Greene, and Marshall's Elements of Steam-engineering 8vo, 3 00 

Thurston's Treatise on Friction and Lost Work in Machinery and Mill 

Work 8vo, 3 00 

Animal as a Machine and Prime Motor, and thfe Laws of Energetics. i2mo, i 00 

Tillson's Complete Automobile Instructor i6mo, i 50 

Morocco, 2 00 

'Warren's Elements of Machine Construction and Drawin:', 8vo, 7 50 

Weisbach's Kinematics and Power ot Transmission. (Herrmann — Klein.) . Svo. 5 00 

Machinery of Transmission and Governors. (Herrmann — Klein.). Svo. 5 00 

Wood's Elements of Analytical Mechanics Svo, 3 00 

Principles of Elementary Mechanics i2mo, i 25 

Turbines Svo, 2 50 

The World's Columbian Exposition of 1893 4to, i 00 

MEDICAL. 

* Bolduan's Immune Sera 12mo, 1 50 

De Fursac's Manual of Psychiatry. (Rosanoff and Collins.) Large i2mo, 2 50 

Ehrlich's Collected Studies on Immunity. (Bolduan.) Svo, 6 00 

* Fischer's Physiology of Alimentation .Large 12mo, cloth, 2 00 

Hammarsten's Text-book on Physiological Chemistry. (Mandel.) Svo, 4 00 

Lassar-Cohn's Practical Urinary Analysis. (Lorenz.) i2n:o, i 00 

* Pauli's Physical Chemistry m the Service of Medicine. (Fischer.) .... i2mo, i 25 

* Pozzi-Escot's The Toxins and Venoms and their Antibodies. (Cohn.). i2mo, i 00 

Rostoski's Serum Diagnosis. (Bolduan.) i2mo, i 00 

Salkowski's Physiological and Pathological Chemistry. (Orndorff.) Svo, 2 50 

* Satterlee's Outlines of Human Embryology i2mo, i 25 

Steel's Treatise on the Diseases of the Dog Svo, 3 50 

Von Behring's Suppression of Tuberculosis. (Bolduan.) i2mo, i 00 

WoodhuU's Notes on Military Hygiene i6mo, i 50 

* Personal Hygiene i2mo, i 00 

Wulling's An Elementary Course in Inorganic Pharmaceutical and Medical 

Chemistry i2mo, 2 00 

METALLURGY. 

Betts's Lead Refining by Electrolysis. (In Press.) 

Egleston's Metallurgy of Silver, Gold, and Mercury; 

Vol. I. Silver Svo, 

Vol. II. Gold and Mercury Svo, 

Goesel's Minerals and Metals: A Reference Book. i6mo, mor. 

* Iles's Lead-smelting i2mo. 

Keep's Cast Iron , , Svo, 

Kunhardt's Practice of Ore Dressing in Europe Svo, 

Le Chatelier's High-temperature Measurements. (Boudouard — Burgess. )i2mo, 

Metcalf's Steel. A Manual for Steel-users. . i2mo. 

Miller's Cyanide Process i2mo, 

Minet's Production of Aluminum and its Industrial Use. (Waldo.). , . . i2mo, 

Robine and Lenglen's Cyanide Industry. (Le Clerc.) Svo, 

Smith's Materials of Machines i2mo, 

Thurston's Materials of Engineering. In Three Parts. Svo, 

Part II. Iron and Steel gvo] 

Part m. A Treatise on Brasses, Bronzes, and Other Alloys and their 

Constituents gyo 

Hike's Modern Electrolytic Copper Refining 8vo, 

MINERALOGY. 
Barringer's Description of Minerals of Commercial Value. Oblong, morocco, 

Boyd's Resources of Southwest Virginia 8vo, 

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Boyd's Map of Southwest Virignia Pocktst-book form. 

♦Browning's Introduction to the Raier Elements 8vo, 

Brush's Manual of Determinative Mineralogy. (Penfield. ) 8vo, 

Chester's Catalogue of Minerals , 8vo, paper, 

Cloth, 

Dictionary of the Names of Minerals 8vo, 

Dana's System of Mineralogy Large Svo, half leather. 

First Appendix to Dana's New "System of Mineralogy." Large Svo, 

Text-book of Mineralogy 8vo, 

Minerals and How to Study Them ; i2mo, 

Catalogue of American Localities of Minerals Large Svo, 

Manual of Mineralogy and Petrography i2mo 

Douglas's Untechnical Addresses on Technical Subjects i2mo, 

Eakle's Mineral Tables Svo, 

Egleston's Catalogue of Minerals and Synonyms Svo, 

Goesel's Minerals and Metals : A Reference Book i6mo, mor. 

Groth's Introduction to Chemical Crystallography (Marshall) i2mo, 

Iddings's Rock Minerals Svo, 

Johannsen's Key for the Determination of Rock-fonning Minerals in Thin 
Sections . ( In P ress. ) 

* Martin's Laboratory Guide to Qualitative Analysis with the Blowpipe, izmo, 
Merrill's Non-metallic Minerals. Their Occurrence and Uses Svo, 

Stones for Building and Decoration Svo, 

* Penfield's Notes on Determinative Mineralogy and Record of Mineral Tests. 

Svo, paper. 
Tables of Minerals Svo, 

* Richards's Synopsis of Mineral Characters i2mo, morocco, 

* Ries's Clays. Their Occurrence. Properties, and Uses Svo, 

Rosenbusch's Microscopical Physiography of the Rock-making Minerals. 

(Iddings. ) Svo, 

* Tillman's Text-book of Important Minerals and Rocks Svo, 



2 CO 
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4 CO 

, I DO 

I 25 

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I oo 

4 oo 
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1 oo 

2 oo 

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2 50 

3 oo 

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4 00 

5 00 

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1 25 
5 00 

5 00 

2 00 



MINING. 

Beard's Mine Gases and Explosions. (In Press.) 

Boyd's Resources of Southwest Virginia Svo, 3 00 

Map of Southwest Virginia Pocket-book form, 2 00 

Douglas's Untechnical Addresses on Technical Subjects i2mo, i 00 

Eissler's Modern High Explosives. Svo. 4 00 

Goesel's Minerals and Metals ; A Reference Book i6mo, mor. 300 

Goodyear's Coal-mines of the Western Coa^t of the United States i2mo, 2 50 

Ihlseng's Manual of Mining. Svo, S 00 

* Iles's Lead-smelting i2mo, 2 50 

Kunhardt's Practice of Ore Dressing in Europe , . . .Svo, i 50 

Miller's Cyanide Process i2mo, i 00 

O'DriscoU's Notes on the Treatment of Gold Ores Svo, 2 00 

Robine and Lenglen's Cyanide Industry. (Le Clerc.) Svo, 4 00 

Weaver's Military Explosives Svo, 3 00 

Wilson's Cyanide Processes , . . .- i2mo, i 50 

Chlorination Process. , , ismo, i 50 

Hydraulic and Placer Mining. 2d edition, rewritten i2mo, 2 50 

Treatise on Practical and Theoretical Mine Ventilation t2mo, i 25 

SANITARY SCIENCE. 

Bashore's Sanitation of a Country House i2mo, i oo- 

* Outlines of Practical Sanitation i2mo, i 25, 

Folwell's Sewerage. (Designing, Construction, and Maintenance.) Svo, 3 00 

Water-supply Engineering. , Svo, 4 00. 

18 



Fowler's Sewage Works Analyses I2m3, 

Fuertes's Water and Public Health i2mo, 

Water-filtration Works i2mo, 

Gerhard's Guide to Sanitary House-inspection i6mo. 

Sanitation of Public Buildings 12mo, 

Hazen's Filtration of Public Water-supplies 8vo, 

Leach's The Inspection and Analysis of Food with Special Reference to State 

Control 8vo, 

Mason's Water-supply. (Considered principally from a Sanitary Standpoint) 8vo, 

Examination of Water. (Chemical and Bacteriological.) lamo, 

* Merriman's Elements of Sanitary Engineering Svq, 

Ogden's Sewer Design i2mo, 

Prescott and Winslow's Elements of Water Bacteriology, with Special Refer- 
ence to Sanitary Water Analysis i2mo, 

* Price's Handbook on Sanitation i2mo, 

Richards's Cost of Food. A Study in Dietaries i2mo, 

Cost of Living as Modified by Sanitary Science i2mo, 

Cost of Shelter . . . . : i2mo, 

Richards and Woodman's Air- Water, and Food from a Sanitary Stand- 
point Svo, 

* Richards and Williams's The Dietary Computer Svo, 

Rideal's S wage and Bacterial Purification of Sewage Svo, 

Disinfection and the Preservation of Food Svo, 

Turneaure and Russell's Public Water-supplies Svo, 

Von Behring's Suppression of Tuberculosis. (Bolduan.) i2mo, 

Whipple's Microscopy of Drinking-water Svo, 

WUson's Air Conditioning. (In Press.) 

Winton's Microscopy of Vegetable Foods Svo, 

Woodhull's Notes on Military Hygiene iCmo, 

* Personal Hygiene iimo. 



MISCELLANEOUS. 

Association of State and National Food and Dairy Departments (Interstate 
Pure Food Commission) : 

Tenth Annual Convention Held at Hartford, July 17-20, 1906. ...8vo, 3 oo 
Eleventh Annual Convention, Held at Jamestown Tri-Centennial 
Exposition, July 16-19, 1907. (In Press.) 
Emmons's Geological Guide-book of the Rocky Mountain Excursion of the 

International Congress of Geologists Large Svo, i 50 

Ferrel's Popular Treatise on the Winds Svo, 4 00 

Gannett's Statistical Abstract of the World : 24mo, 75 

Gerhard's The Modem Bath and Bath-houses. (In Press.) 

Haines's American Railway Management i2mo, 2 50 

Ricketts's History of Rensselaer Polytechnic Institute, 1S24-1SQ4. .Small Svo, 3 00 

Rotherham's Emphasized New Testament Large Svo, 2 Oo 

Standage's Decorative Treatment of Wood, Glass, Metal, etc. (In Press.) 

The World's Columbian Exposition of 1893 4to, i 00 

Winslow's Elements of Applied Microscopy i2mo, i 30 



HEBREW AND CHALDEE TEXT-BOOKS. 

Green's Elementary Hebrew Grammar i2mo, i 23 

Hebrew Chrestomathy Svo, 2 00 

Gesenius's Hebrew and Chaldee Lexicon to the Old Testament Scriptures. 

(Tregelles.) Small 4to, half morocco, 3 00 

Letteris's Hebrew Bible Svo, 2 23 

19 





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